White’s last move was 41.Be2-c4, probably counting on 41...Bxc4 42.Rxc4 Qd6. The position had been absolutely equal, and, losing concentration, White probably thought he could draw however he liked, so he carelessly offered the exchange of bishops. However, he forgot about the back rank, and there followed:

There is no defence against the threat of ...Ra2-a1, and Black mates first!

42.Bxe6 Ra1 43.Bxf7+ Kg7–+.

White resigned.

Because of the back-rank mate, the queen is immune, and her sudden inclusion in the attack immediately decides the outcome of the game.

22...Qb6 23.Qxh7 Rf8 24.Rb3+–.

23...Rf8 24.Nxd4+–.

In the game, White missed this chance, and after 22.Rd3 Bxh4 23.Nxh4 Rxb5 24.axb5 Ne5, Black had the initiative and went on to win.

Black does not threaten any dangerous checks and, more importantly, has no mating threats. Meanwhile, his bishop and central pawn are hanging, and the former cannot move away. It seems time to resign, and the only question is whether he can pose a threat, given that the entire white army has advanced a long way forward, leaving his king unprotected. And there is indeed such a possibility – moreover, it lies on the surface: