The d4-pawn is isolated and needs defending. Black exploits this:

The weakening of a whole group of dark squares, which this move forces, is very significant, especially in view of White’s lack of a dark-squared bishop.

19.g4 Bf7 20.bxc6 Rc8 21.Qb2 bxc6 22.f5 Qd6 23.Ng2

An attempt to cover the square f4 against an entry by the black queen. But the knight is badly placed here, because it does not perform any other functions. White’s problems are growing.

Including yet another piece in the attack on the dark squares, decides the game.

29.Nxg5 Qh2+ 30.Kf1 fxg5–+.

White resigned.

There is a lack of coordination among the white pieces. Exploiting this, Black creates an object of attack on the queenside:

He should not allow Black to open lines for his rooks; instead, he should prefer 20.bxa5 bxa5 21.Nd4, with chances of equalising.

More active is 22.Nc3, after which Black’s advantage is minimal.

The pawn stands slightly more actively, taking c4 from the white knight, and opening a path to b6 for the bishop.