Sunday, March 20, 2011

Avoiding an Opposite-Colored Bishop Ending Through an Exchange Sacrifice

Opposite-colored bishop endings are notoriously (or wonderfully, if you are the defender) drawish.  One side can frequently have two, or even more, extra pawns but absolutely no chance of winning, because it cannot overcome a blockade on the squares that its bishop does not cover.  Dvoretsky gives the following example:


Despite being up three pawns, Black cannot win.  White merely moves his bishop along the h3-c8 diagonal.

If there is more material on the board, one way for the side with the advantage to avoid this fate is to sacrifice some material.  The Tata Steel tournament earlier this year witnessed two nice examples of this stratagem.

In Navara-Ganguly, from Round 6 of the B Group, is perhaps not the best example, as White is probably winning even in the rooks plus opposite-colored bishops ending that arose in the following position:

Navara-Ganguly, after 34...Rxb8

But rather than start pushing his queenside pawns, leaving open the possibility that Black might establish a dark-square blockade, Navara played the elegant:


And Ganguly resigned.  After 35...exf4, either 36.a6 or 36.b4 will force Black to sacrifice his rook for one or two pawns, leaving White with an easy win.

Next L'Ami-Wang Hao, from Round 10 in Group A, reached the following position:

L'Ami-Wang, after 45.Bb5

Black is up two pawns, but White has just played 45.Bb5, blocking the b-file and intending to win back one pawn on b3.  There is again the prospect of a long struggle to grind out a win despite the opposite-colored bishops.  Black avoided this by playing:

45...Rxb5! 46.axb5 a4!

L'Ami-Wang, after 46...a4!

 Now the connected passed pawns paralyze the White rooks.  The White passed b-pawn is easy to stop.

47.b6 Rb4 48.Ra1 Otherwise Black plays ...Rxb6.  48...Bd6 Covering the b-pawn's queening square and also threatening Be5, skewering the rooks.  49.b7

White can't rearrange his rooks.  If 49.Rab1, then 49...a3! 50.Rxb3 Rxb3 51.Rxb3 a2 and the pawn can't be stopped.  If White tries for activity by 49.Rd1, then again 49...a3 50.Rbb1 a2, again winning.

L'Ami-Wang, after 49.b7


Wang plays it extra safe, not allowing even a hint of counterplay or risk.  But the more direct 49...Kf8 and 49...Be5 would also have won.  For example, after 49...Be5, White has to give up a rook for the pawns: 50.Rxa4 Rxa4 51.Rxb3 Bb8.  This variation required a bit of calculation, to make sure that White can't get his rook to the back rank or support the b-pawn with his king after the exchange of rooks, but Black wins easily in all variations:

a. 52.Rc3 Rc4 53.Rxc4 dxc4 54.Kf3 Kf8 55.Ke4 Ke7 and the Black king arrives in time.
b. 52.Re3 Kf8
c. 52.Kf3 Kf8 53.Rd3 Rb4 54.Rxd5 Rxb7

Wang's move also wins, however.

50.f4 Kg6 Black simply walks his king to the queenside to capture the b-pawn and then support his own pawns.  51.Kf3 Kf6 52.Ke3 Ke6 53.Kd3 Kd7  0-1

L'Ami had had enough, and resigned.  Play could have continued 54.Kc3 Rc4+ 55.Kd3 Kc7 56.Rxa4 Rxa4 57.Rxb3 Rb4.

No comments:

Post a Comment