White needs to develop his play on the queenside. If he begins the preparation for the advance of the b-pawn with the move a2-a3, then after b2-b4 he will need further preparation of the advance b4-b5 with the help of the a-pawn, and will have to spend additional time defending b4. Foreseeing this, White chose...

Played in one move, and winning a precious tempo.

Under cover of the powerfully-entrenched knight, White easily demolishes the black defences.

Black resigned.

For a successful attack, White needs to open lines on the kingside. For the sake of this, he sacrifices a bishop:

Not only attractive, but effective. 18.g6 would keep a strong initiative, but allows Black, after 18...h6, or 18...fxg6 19.hxg6 h6, to somewhat fortify the approaches to his king.

19...fxg6 20.Nxe4 dxe4 21.Ng5++–.

20...Qxe4 21.gxf7+ Kxf7 22.Ng5++–.

Other moves also lose:
A) 21...exf3 22.gxf7+ Qxf7 23.hxg7!;
B) 21...fxg6 22.Nh4! g5 23.h7+ Kf7 24.Nf5 Qe6 25.Rxg5 g6 26.Rh6+–;
C) 21...f5 22.Qxc4+ Qe6 23.Qxe6+ Rxe6 24.Ng5 Rf6 25.Nf7 gxh6 26.Rxh6+–.

Black resigned.