Prophylaxis · For club players · 13 min read
Prophylaxis: Karpov's 24.Ba7 Against Unzicker, Checked by Stockfish
Karpov's quiet bishop move at Nice 1974 is the textbook case of prophylaxis. Stockfish 19 says the move was the only good one, and that the game was decided later, by Black's 31...g5.
- plan
- key square
- The sealed a-file
- Black's cramped camp
- pawn chain or line of force
In short
- Prophylaxis means asking what the opponent wants before executing your own plan, and stopping it quietly.
- In Karpov against Unzicker, Nice 1974, White's 24.Ba7 shut the one open file Black needed, and White then opened the kingside with f4.
- Stockfish 19 says Ba7 was the only move that kept an edge, worth about a pawn, and that Black's 31...g5 gave away more than two pawns.
- The lesson for club players: find the opponent's best plan, make one move that stops it, then break where the opponent has no counterplay.
How we know what we say
- Verified From the record: Stockfish's numbers, the players' own notes or interviews, or a cited source.
- Inferred Read from the moves and the position: a reasoned reconstruction, not the player's words.
- Speculative A guess about mood, intent or practical motives: plausible, not proven.
Part 1Nice 1974: Karpov meets the German board one
In June 1974 Anatoly Karpov was 23 and had not yet won the world title. Karpov would become world champion in 1975, when Bobby Fischer did not defend the title. At the 21st Olympiad in Nice, Karpov played board one for the Soviet Union against West Germany and its veteran grandmaster Wolfgang Unzicker. [5][6] Verified
The score comes from two sources that agree on every move: chessgames.com and a shared ChessBase file. A third site, 365Chess, prints Black's 43rd move as ...Kh8; the other two have ...Kf8, and so does this article. The round and date differ too: chessgames says round 4, 18 June, ChessBase round 3, 17 June. [1][2][3] Verified
| Item | Detail |
|---|---|
| Game | Karpov vs Unzicker, Nice Olympiad Final-A 1974 |
| Opening | Ruy Lopez, closed, Chigorin Defence (C98) |
| Result | 1-0 in 44 moves |
| Strategy | Prophylaxis: stop the opponent's plan before pushing your own |
Part 2What is prophylaxis in chess?
Prophylaxis is a move or plan whose main job is to stop the opponent's best idea. Instead of asking only what you want, you ask what the opponent wants, and spend a move taking it away when it is the most important thing on the board. It works best when the opponent has exactly one good plan, and worst when you are already behind in a race.
- threat
- target
- key square
- Black's only open file
- outpost
- key square
- Sealed by the bishop
- pawn chain or line of force
The same position, before and after the prophylactic move. On the left Black threatens to trade rooks and own the a-file; on the right one bishop move makes the trade lose the exchange.
Notice what the bishop move does not do. It does not attack, does not win a pawn, and does not threaten anything on the next move. Its only effect is that a plan Black wanted no longer works, which is why prophylactic moves look strange to players who judge a move by what it threatens.
Part 3How the opening built the structure
Karpov chose the closed Ruy Lopez against Unzicker's Chigorin set-up, with ...Na5 and ...c5. The line runs 9.h3 Na5 10.Bc2 c5 11.d4 Qc7 12.Nbd2 Nc6 13.d5, and the centre is locked: White's pawns on d5 and e4 against Black's on d6 and e5. A locked centre means the game is played on the wings, and plans, not tactics, decide it.
13...Nd8 14.a4 Rb8 15.axb5 axb5 16.b4 Nb7 +0.64White slightly better
13.d5 and the exchange of the a-pawns open the a-file. Both sides' rooks will contest it, so the file becomes the pivotal feature of the game. Inferred
- key square
- outpost
- The only open file
- pawn chain or line of force
The a-file is the only open file on the board. In a locked position the side that controls the only open line usually has the safer game, so each side's first plan is the same: use the a-file. White's rook stands on a2, Black's on a8, and the question is who will be allowed to trade them.
Part 4Two plans from the same position
The structure points both players toward the same squares. White wants to break open the kingside with f4 and use the knights, while Black wants counterplay on the f-file or on the queenside. The difference is that White has already stopped Black's queenside plan.
- plan
- key square
- White's kingside play
- idea not played
- key square
- target
- Black's resources
White's plan on the left (f4 with knights on g3 and f3 or g4); Black's best answer on the right (...exf4 and a grip on e5).
Part 5The moments that decided the game
Three of Karpov's decisions show the strategy: the prophylactic move, a loosening waiting move, and the break that finally opened the game.
Critical moment 1 of 4 · Move 24, White to play
Which plan do you start: yours or the opponent's?
- threat
- target
- Black's file
White would like to play on the kingside, but Black's rook on a8 stands opposite the one on a2. Before choosing a plan, what does Black want to do next, and how do you stop it?
Think it through on the boardWeigh the candidates
| Move | Stockfish | Verdict |
|---|---|---|
| 24.Rc2 24...Ne8 25.Nh2 | 0.00about equal | Level in Stockfish's view. Rc2 leaves the file open and Black keeps the rook trade in reserve. Verified |
| 24.Rxa8 24...Rxa8 25.Ng5 | +0.13about equal | About a tenth of a pawn for White. Trading the rooks leaves the file to Black's remaining rook and the edge almost disappears. Verified |
| 24.Ng5 24...Rxa2 25.Qxa2 | 0.00about equal | Level. Black answers ...Rxa2 Qxa2 and is the one who controls the file. Verified |
What Karpov played
24.Ba7+1.08White clearly better
Karpov plays Ba7, putting the bishop between the rooks. Black cannot take on a7 without losing the exchange, so the trade of rooks on a2 never happens.
Stockfish's first choice too. Depth 26.
What it revealed
The move does not attack anything. It removes Black's one active plan and leaves White's rooks free to double behind the bishop later. That is prophylaxis: the quiet move is a reply to a threat that had not yet been played.
What Stockfish adds Ba7 is the only move that keeps an edge: Rc2, Rxa8 and Ng5 all leave the game level or within a tenth of a pawn of it. The edge Ba7 keeps is about one pawn, so the exclamation marks of popular accounts are earned by the idea, not by a decisive gain.
- Verified Soumya Swaminathan's 2025 column in the Free Press Journal calls 24.Ba7 a prophylactic move that stopped Black's idea on the a-file.[4]
- Verified Stockfish agrees: Ba7 is its first choice, worth about a pawn, and if White passed, Black's best move would be ...Rxa2 with equality.
- Inferred The other tries leave the a-file open, so Black keeps the rook trade as a resource: only Ba7 takes it away.
Critical moment 2 of 4 · Move 27, White to play
Waiting move or improving move?
- key square
- Bishop's retreat squares
White is better, with Black's a-file closed and the knights not yet on their best squares. White's bishop on c2 has been shuttling. Which piece should move first?
Think it through on the boardWeigh the candidates
| Move | Stockfish | Verdict |
|---|---|---|
| 27.Bd1 27...Nd8 28.Bb6 | +1.27White clearly better | Stockfish's choice, about a pawn and a quarter. The bishop heads for the kingside and Bb6 stays in the air. Verified |
| 27.Ne1 27...f6 28.Bd1 | +1.19White clearly better | About a pawn and a fifth: better than the move played, a little worse than Bd1. Verified |
| 27.Nh2 27...Nd8 28.Bb6 | +1.33White clearly better | About a pawn and a third: the knight moves toward f4 and the edge stays above the move played. Verified |
What Karpov played
27.Bb1+0.81White slightly better
Karpov plays Bb1, and Black answers by bringing the bishop to e8.
Stockfish preferred 27.Bd1 (+1.45); the game move gave up about 0.6 pawns. Depth 24.
What it revealed
This is the least convincing moment of the game from the winner, and it matters: a prophylactic plan still has to be improved on every move. The bishop move did not lose the advantage but cost about half a pawn against the best move.
- Verified Stockfish rates Bb1 below the best move by about half a pawn; White's edge shrinks from about a pawn and a half to under a pawn.
- Inferred The bishop returns to b1, the square it left on move 25, so the move improves nothing.
- Speculative Karpov may have been in no hurry because Black had no active plan, so the waiting move cost little in practice.
Critical moment 3 of 4 · Move 30, White to play
The moment to break
- idea not played
- key square
- target
- White's lever
White's pieces are on their posts, the queenside is sealed, and Black has just placed the bishop on g7. Waiting more would give Black time to untangle. Is there a break, and which?
Think it through on the boardWeigh the candidates
| Move | Stockfish | Verdict |
|---|---|---|
| 30.Ra5 30...f6 31.f4 | +0.94White clearly better | About a pawn: more than half a pawn less than f4. The break is delayed and Black gets ...f6. Verified |
| 30.Bc2 30...f6 31.f4 | +0.96White clearly better | About a pawn. Another waiting move, and Stockfish prefers the break at once. Verified |
| 30.Ng3 30...f6 31.Bc2 | +0.91White clearly better | About a pawn. The knight is well placed on g3, but f4 is worth more than half a pawn more. Verified |
What Karpov played
30.f4+1.54White clearly better
Karpov plays f4 now. If Black takes with ...exf4, the knight recaptures on f4 and Stockfish keeps White clearly ahead, while the bishop on a7 keeps the queenside under control.
Stockfish's first choice too. Depth 25.
What it revealed
The break comes only after the prophylaxis is done: Black has no counter on the queenside, so opening the kingside costs White nothing. Prophylaxis buys the time to open the second front on your terms.
- Verified Stockfish picks f4 by a clear margin: it rates the position after f4 at about a pawn and a half, against about a pawn for the quieter moves.
- Inferred f4 is playable because the bishop on a7 and the rooks on a2 and a1 keep the queenside shut, so opening the centre gives Black no file.
Part 6The turning point: 31...g5
After 30.f4 f6 31.f5 White has a space advantage on the kingside, and Black has a decision. Black can keep the structure flexible or end it with a pawn move. The game is short of tactics from here, and the choice of structure decides it.
Critical moment 4 of 4 · Move 31, Black to play
Close the position or defend the pieces?
- threat
- target
- Black's kingside
White's pawn on f5 attacks the pawn on g6. Black is worse but has no loose piece. Which keeps more chances: a pawn move that closes the structure, or a piece move that keeps the options open?
Think it through on the boardWeigh the candidates
| Move | Stockfish | Verdict |
|---|---|---|
| 31...Nf7 32.Ng3 Bh6 | +1.78White clearly better | Stockfish's choice. White keeps about a pawn and three quarters, but the structure stays flexible and Black has resources. Verified |
| 31...Bd7 32.Ng3 Nf7 | +2.17White winning | About two pawns and a bit for White: worse than Nf7 but far from the damage of the move played. Verified |
| 31...Qf8 32.Ng3 Bh6 | +2.43White winning | About two and a half pawns for White: passive, but the structure is not closed. Verified |
What Unzicker played
31...g5+4.15White completely winning
Unzicker plays g5, shutting the kingside for good. White's f5 pawn can never be challenged and becomes a permanent space gain.
Stockfish preferred 31...Nf7 (+1.86); the game move gave up about 2.3 pawns. Depth 22.
What it revealed
g5 tries to stop the loss of a pawn and instead removes the last of Black's own breaks: ...g6 and ...gxf5 are gone, and White can regroup without worry. The engine swing is more than two pawns.
What Stockfish adds This is the decisive error: ...g5 is more than two pawns worse than ...Nf7. The famous 24.Ba7 kept about a pawn; ...g5 handed over more than twice that.
- Verified Stockfish rates the position after 31.f5 at about a pawn and three quarters for White and after 31...g5 at about four pawns.
- Verified The ChessBase notes by Martin call Black positionally outplayed by the end of the game.[2]
- Inferred After g5 the pawns on f6 and g5 hem in Black's own bishop on g7, which has only h6, f8 and h8 left, and nothing can challenge the f5 pawn.
44...Bh8 45.Qxh6+ Ke7 46.Ng4 +7.57White completely winning
After 44.Nh5 Black resigned rather than face Qxg7 mate. Moving the bishop avoids the mate but loses the h6 pawn with check and the attack continues. Verified
- threat
- target
- key square
- Black's king
Part 7What Black could have done
Black was worse, but not lost. The saving idea was to keep the pieces flexible and avoid making a pawn move that cannot be taken back.
- idea not played
- outpost
- key square
- Black's kingside regroup
31...Nf7 32.Ng3 Bh6 33.Qf2 Bg5 34.Nf3 Bh6 35.h4 +1.78White clearly better
Stockfish's defence: the knight to f7, then the bishop on the h6-g5 route. White keeps an edge, but Black's pieces stay active. Verified
Part 8What Stockfish says that the usual account misses
The usual account gives 24.Ba7 as the decisive prophylactic stroke. Stockfish agrees that Ba7 was best, indeed the only move that kept an edge, but the position stood at about a pawn for White before and after it, so the move is better described as a first step. The collapse came seven moves later with 31...g5.
| Move | What changed | Edge for White |
|---|---|---|
| 24.Ba7 | The a-file is sealed; rook trade prevented | about +1.1 |
| 27.Bb1 | Karpov gives back part of the edge | about +0.8 |
| 30.f4 | The break begins | about +1.5 |
| 31...g5 | Black closes the position | about +4.2 |
Part 9How to use prophylaxis in your games
The recipe
- Find the opponent's planImagine passing. Which move would the opponent play, and does it improve their position much?
- Rate the dangerIf the opponent's idea gives equality or a strong initiative, deal with it first. If it is harmless, continue your own plan.
- Choose the quietest stopLook for a move that makes the idea fail tactically or positionally, as Ba7 made ...Rxa2 lose the exchange.
- Improve your piecesOnce the main plan is stopped, place the pieces on their best squares before breaking.
- Break where the opponent has no counterOpen the position on the wing where the opponent is weakest.
- What would the opponent play if I passed?
- Is that move strong enough to stop?
- Is there a move that stops it and improves a piece?
- After it, where can I break?
Your turnPractise it
Set each position up, decide your plan before you look, then play it out against Stockfish to see whether it holds.
White to play. Black threatens to trade rooks on a2 and take the a-file. Find the move that stops it.
Hint
A piece can go between the rooks.
A good answer
Ba7. The bishop blocks the file; ...Rxa7 Rxa7 wins the exchange.
White to play. The queenside is sealed and the pieces are set. Which pawn move opens the game?
Hint
The pawn on f2.
A good answer
f4. Stockfish gives it a clear lead over the quieter moves.
Black to move after 31.f5. Choose between a closing pawn move and a piece move that stays flexible.
Hint
Which move keeps more of Black's options?
A good answer
Nf7. The knight keeps the structure flexible, while the pawn move g5 costs more than two pawns.
Part 10Takeaways
- Ask the pass question. What would the opponent do if you passed?
- Stop the one plan. The quiet move beats a flurry of ideas.
- Keep improving. A prophylactic move is a start; a waiting move can cost half a pawn.
- Break last. Open the second front after the first is sealed.
- As a defender, keep options. A closing pawn move can lose two pawns of evaluation at once.
Questions readers ask
What is prophylaxis in chess?
Prophylaxis is a move or plan that prevents the opponent's best idea before it happens. Instead of attacking, you take away the square, file or break the opponent wants, as Karpov did with 24.Ba7 against Unzicker.
Who invented prophylactic thinking?
Aron Nimzowitsch made prophylaxis a central idea of the chess system Nimzowitsch taught in the 1920s, and Tigran Petrosian and Anatoly Karpov later became its best-known practitioners.
Was 24.Ba7 really the best move?
Yes, Stockfish 19 picks 24.Ba7 as the best move, and the other tries leave the game level, but the advantage it keeps is about a pawn. The game was decided later, by Black's 31...g5, which cost more than two pawns.
How do I practise prophylaxis?
Before every move in training games, write down what your opponent would play if you passed. If that move would be strong, find a quiet move that stops it. After a few weeks the question becomes automatic.
Is prophylaxis only for positional players?
No. Tactical players use it too, to remove a defender's resource before a combination. The habit of asking what the opponent threatens is useful in every kind of position.
Sources and method
The game score was checked against two independent sources. Every position, line and candidate in this article was replayed for legality, and every engine number was produced by Stockfish 19 WASM Multithreaded for this article (depth 18 to 33, deepest at the critical moments), not copied from elsewhere. What the players thought is reconstructed from the moves, their published notes and later analysis; it is labelled as verified, inferred or speculative, and nothing is presented as a quotation unless a source is cited for it.
- chessgames.com: Karpov vs Unzicker, Nice 1974 (PGN)
- ChessBase shared game: Karpov - Unzicker 1974 (annotations by Martin)
- 365Chess: Nice ol (Men) fin-A 1974 (prints 43...Kh8)
- Free Press Journal: Chess, how to think like your opponent (2025)
- Wikipedia: Anatoly Karpov
- ChessBase Modern Classics: Karpov - Unzicker 1974
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Strategy sticks when you use it. Practise real positions with Stockfish's verdict at once, or play the plans out from any diagram above.