Not an innocent bystander, but one exerting annoying pressure against g7, together with the b2-bishop!

19...Rf7

21...exf4 22.f5 Ne5 23.f6

White's strong pressure against Black's kingside gives him . a clear advantage. Postny elegantly converted this.

Improving the position of the bishop.

Otherwise the beastly bishop will dominate both white rooks on d3 .

Now White slipped up with . . . .

. . . and lost quickly after . . .

Reaching for the hole on d6 to become an octopus.