World Champion Tigran Petrosian is well known for his positional exchange sacrifices. A less known strategic idea that appeared in several of his games is the bishop exchange for the c3 knight in the King's Indian Defense (KID). In the KID, the dark-squared bishop is one of Black's most valued pieces. Sometimes Black goes a long way and sacrifices the e5-pawn just to free the way for the g7-bishop. When planted on e5 or f4 the bishop usually participates in deadly KID attacks.
Therefore, it is paradoxical to exchange the monster on g7 for seemingly less of a piece - Nc3. The main idea of this exchange is to double the white pawns on the c-file, which will significantly restrict the movement of White's dark-squared bishop. Today's article will cover this strategic idea, which is closely related to bishop restriction methods we explored in the last two articles.
The first example is from a world champion's practice. Petrosian gave up his dark-squared bishop for Nc3 but got equal play with the black pieces. Key ideas to pay attention to:
- Bxc3 works if the only way White can recapture is bxc3;
- Black must have a pawn on c5, otherwise, if White's bishop gets to d4, Black's position will collapse;
- Black has to be ready to meet the g4-break;
- White will most likely combine the threat of the g4-break with expansion on the queenside.
David Bronstein played very carefully as White and so the game quickly ended in a draw. The next example shows how a premature g4 can weaken White's position; after an trade on g4, one might end up with a weak pawn on f4 and Black's knights will have an excellent outpost on f5, from where they can threaten the e3-square. This square is very important because the movement of Black's passed e-pawn can be very dangerous for White. Petrosian outplayed his opponent but did not find the final tactical idea and let Dutch GM Jan Hein Donner escape.
The next example is from modern play. So far, we saw Black responding to White's plans. But what to do when White is simply waiting and is happy with a draw? In the following game the rating difference between the players is more than 200 points, hence naturally Black wants to create some play to have winning chances. Here we see one of the key ideas for Black in these structures: play on the queenside. Black was threatening a b5-break and tied the white forces on the queenside and then he exchanged his light-squared bishop, which was locked behind the f5-pawn. He used what is a common maneuver in the Dutch Defense: Bd7-e8-h5.
The dangers that Black can face if playing in gambit-like style are shown in the following game. Korobov sacrificed his e-pawn to get the e4-square for the knight. However, it turns out that the knight is not really safe on this square as it can be undermined with the g4-break. Since White has not yet played g4, he solidified with the g3-move and got a position with an extra pawn.
The last position is from one of the KID lines analyzed by Viktor Bologan in his excellent book King's Indian: A Complete Black Repertoire. This position is different from what we considered so far as there is no white pawn on f4 to block the range of the dark-squared bishop's movement. With his g5-push, Black effectively takes away the f4-square from the bishop and thus limits its range. This g5-move is essential in most of the lines analyzed in this type of position.
Next week's article will be once again about classic heritage in modern play.