A brilliant decision! Black solves all his problems, which consist of his inactive bishop, blocked by the enemy pawns, and his lack of space. The connected passed pawns created by the sacrifice are joined by the d5-pawn, and form a dangerous avalanche. The pawns have a long way to go to promote, and therefore Black had to realise that the position is fairly closed, and the white knight cannot organise counterplay on the kingside.

By playing 40...b4!?, it was possible to pose White greater problems.

Passive defence on the queenside does not lead to any happiness, and so White seizes the first chance for counterattack, which proves to be the saving resource.

This could also have been delayed until the next move, when the black rook stands on b5, but Black decided not to fight against the inevitable.

Similar positions frequently arise in the Queen’s Indian Defence, and the device used now by White is a typical one:

In this case, the knight jump leads to a gain of material, but sometimes it is played just with the intention of transferring the knight to a5 or e3, or to attack an enemy queen on b6, exploiting tactical motifs as the knight cannot be captured, because the d5-pawn is pinned along both file and diagonal.

And White won.

Black has the advantage of the two bishops and his pieces are actively placed, excellently supporting his pawn duo. Now, there follows a break, which crowns Black’s build-up:

25.exd4 Bc6! 26.Qc4 Bxf3 27.gxf3 cxd4 28.Na4 Qb5 29.Qe2 Rc7! 30.b3 Qxb3 31.Qxa6 Qxf3 also offers no hope of survival.

The white pawn islands on dark squares are indefensible.