Today we continue our series on positional exchange sacrifices. Last week we saw some examples of exchange sacrifices to create a general situation which benefits the minor pieces. This week we will be focusing on examples of exchange sacrifices with the purpose of creating a blockade.
Sacrificing the exchange to create a blockade is a fairly common stratagem. The reason that this method can work well is that in addition to obtaining a blockade (i.e. shutting down your opponent's pawn breaks and installing a piece on a strong square) you simultaneously create a position where the rooks do not work as well - a closed position with fewer open lines. Here is a classic and very well-known example, from the master of the positional exchange sacrifice, Tigran Petrosian:
Black seems to be in trouble. He is facing the threat of Bf3 followed by d4-d5, after which the pawns will sweep away everything in their path. But Petrosian now played 25...Re6!!
This move appears to simply put the rook en prise to the lower-valued white bishop. But it also does several other things. First of all, it opens the e7 square for the black knight. Thus Black succeeds in time to blockade the d5 square. For example, if White refuses the exchange sacrifice and continues with his plan by 26.Bf3, then comes 26...Ne7 and Black will succeed in placing the knight on the ideal d5 square, blocking the white pawns.
Meanwhile, if the sacrifice is accepted, a couple other things are accomplished. Black, by recapturing with 26...fxe6, moves his f-pawn to the better place on e6, where it helps to control d5 and blocks the white e-pawn firmly. And finally, the acceptance of the sacrifice requires White to give up his light-squared bishop. Since his pawns in the center will be blockaded on dark squares, White will be woefully short of light-square control. This will allow Black to maintain a tight hold on the position.
White actually played 26.a4, trying to ensure that some lines opened before accepting the exchange sacrifice. Black had good chances throughout the rest of the game, which ended in a draw. For illustrative purposes, let's see what might have happened had White simply taken the "free" exchange. After, for example, 26.Bxe6 fxe6 27.Rf3 Ne7 28.Ref1 Nd5 29.Qd2 Qe7, the following position arises:
It is clear that all of the previous dynamism of White's position is gone. His center pawns are completely blockaded and he cannot challenge on the light squares. He is up the exchange, but there is no way for the rooks to invade, since there are no targets on the f-file and the half-open b-file is also not useful. The knight on d5 is a great force which blocks the d-pawn, keeps c3 constantly under attack, and also covers other important squares. Meanwhile the bishop on b2 is pathetic.
Although it is not clear that Black actually stands better, it is easier to see a way for him to potentially play for a win, most likely by somehow arranging ...b5-b4 under good circumstances. In any case, even if the position is only equal, it is clear that Black has made great strides with his exchange sacrifice, since otherwise the position seemed to be desperate.
Another very typical blockading exchange sacrifice occurs when there is an open file where one side has an outpost which is nevertheless covered by an opposing minor piece. In this case, the player may put the rook on that outpost anyway, allow it to be taken and then recapture with a pawn. This creates a passed pawn, usually frees up a blockading square for a knight, and simultaneously closes the formerly open file, creating a situation where the rooks can't function right. Here is a classic example:
I apologize for the last two examples, which many of you might have already seen before. The following you won't have seen, and shows the same kind of idea as Alekhine used.
Finally, we will see a couple of beautiful examples where a player sacrifices the exchange in order to create a blockade position over the whole board. In the resulting position, the opponent is left with a useless bishop which can neither defend nor attack, while the rooks have no relevant open lines. The attacking side's knights, on the other hand, have a tempting choice of different outposts and can attack various pawns.
The first example is Tomashevsky-Ponomariov, from Rogaska Slatina 2011. Right out of the opening White sacrificed the exchange to create a position where his knights dominated the opposing bishop and rooks.
And finally, a positional masterpiece by Yasser Seirawan, in which he makes a far-sighted exchange sacrifice to completely blockade the black position. Black has the extra material, but cannot do anything with it, and the knight hops from outpost to outpost, terrorizing Black's blockaded pawns.