Chess Stack Exchange is a question and answer site for serious players and enthusiasts of chess. It only takes a minute to sign up.
Sign up to join this community
[FEN "1r1q1rk1/p4pp1/3p1b1p/2pQ4/4P3/P1P2P2/1P2B1PP/1K1R3R b - - 0 20"]
[Title "The Position"]
1... Bxc3??
In this position, I believed that the best move for Black is Bxc3. It’s a free pawn, creates a threat on b2, and exposes the white king.
However, Stockfish labels it a blunder. The advantage goes from around −2.5 to −0.5.
After Black plays Bxc3, Stockfish suggests the move b3 for White. I do not see how this justifies labeling the bishop move a blunder.
Because you have opposite-colored bishops and it's nearly impossible to win in the endgame. You can, however, take advantage of the weak white king.
After 20... Bxc3 the game will most likely continue:
[FEN "1r1q1rk1/p4pp1/3p1b1p/2pQ4/4P3/P1P2P2/1P2B1PP/1K1R3R b - - 0 20"]
1... Bxc3 2. b3 Bd4
This will you protect your pawn on d6. You've lost your chance to win now.
20... Qa5 or, even better, 20... Qb6 begins the attack. Here's a possible (and interesting) continuation:
[FEN "1r1q1rk1/p4pp1/3p1b1p/2pQ4/4P3/P1P2P2/1P2B1PP/1K1R3R b - - 0 20"]
1... Qb6 2. Qd2 Qb3 3. Ka1 Bg5 4. f4 Bxf4 5. Bc4 Bxd2
6. Bxb3 Bxc3 7. Bxf7+ Rxf7 8. bxc3 Rf2
The bishops are gone and your opponent's pawns are split. You also threaten to move your other rook on the second rank.
Positions with opposite color bishops and heavy pieces are known to be very complicated and double-edged. The tension between two sides can last for a long time because of continuous maneouvering of rooks and queens.
Consequently, evaluation of the position depends mostly on the dynamical resources and weaknesses in pawn structure and not on just pawns counting (but of course it counts too). After 1. ... Bxc3 2. b3 and subsequent Bc4, Ka2 White hampered black's attack along the b-file. And it's not clear for black how to proceed.
At the same time white has a clear plan of advancing king's side pawns evolving the attack. f7 pawn is pinned and it would be a long-term target for white's pieces on light-squared diagonal a2-g8.
I think, that exchanging off queens will bring white's edge in the endgame.
To see more deeply we can make intermezzo move 1. ... Qb6 threatening mate. Now b3 can not be played. And white needs to play 2. Qd2 to protect c3 and b2. Then black's idea to put all his heavy pieces along b-file and continue attack. White is in trouble because his bishop can not take part in defense, for example:
[FEN "1r1q1rk1/p4pp1/3p1b1p/2pQ4/4P3/P1P2P2/1P2B1PP/1K1R3R b - - 0 20"]
1...Qb6 (1...Bc3? 2. b3 Qb6 3. Bc4=) 2. Qd2 Qb3 3. Ka1 Bg5! (3...Rb6 {with idea of Rb8. With edge for black.}) (3. Qc2? Bxc3 4. Qb3 Rb3 5. Kc2 Rxb2 6. Kxc3 Re2) (2... Rb7 3. Bc4 Rfb8 4. b3 Qa5 {targeting a3 and c3. Also good for black strategically.}) 4. f4 Bf4 5. Bc4 {only move} Bd2 6. Bb3 Bc3 7. Bf7 Rf7 8. bxc3 Rf2 {with very good chances in the endgame for black}
Main line of my variations is from previous answer by double-beep.
The pawn is actually a goner in any case after 1...Qa5 or 1...Qb6 - White can't play 2.c4 since Black can play Rxb2+, breaking the pin with 2. Kc2?? or 2. Kh2?? leads to 2...Rxb2+ 3. Kxb2 Qxc3+ and checkmate, and the pawn is attacked more times than it can be defended.
The real difference is that if you take the pawn immediately, White can play 2. b3 followed by 3. Ka2, which leads to a solid defensive set up against which you don't have immediate attacking ideas. This is why Stockfish wants to play 1...Qa5 or 1...Qb6, preventing this defense, before taking the pawn.
Note that although 1...Bxc3 wins a pawn, you still aren't actually ahead in material because in the current position you are a pawn down, and White has positional trumps as well - in particular your d6-pawn is weak and it's hard to eject the Queen from d5.
It's not so much that Bxc3 is a blunder, as that not doing Qd6 is a blunder. Stockfish gives +4.5 to this position with White to move, and -0.4 after Bxc3, so Bxc3 compared to nothing at all improves your position by 4.1. It's just that Qd6 improves your position even more. Even if a move doesn't give up material, keep in mind that every move costs a tempo. Opportunity cost is just as important as direct cost, and an opponent's weakness left unexploited is just as much a blunder as giving yourself a weakness. "When you see a good move, look for a better one."
