Annotated chess game

Maybe White could have considered letting the c-pawn go: 21.Rcd1 Bxc4 22.e6! ... But Black might simply have castled: 21.Rcd1 0-0 22.Nb5 Rxc4 23.Nxa7 Rb8 ... Note that 21.Be3 Bxe3 22.Rxe3 0-0! would not not have solved White's problems, either, committed as he is to defending the problem child on c4.

Another idea was to castle, to prevent possible discoveries against the h8-rook.

Black's position was too good seriously to consider taking the draw!

Black could have castled here. White isn't threatening much, so Black could have taken the time.

Good enough, I think, but White could equally well have solved his c-pawn problem at once by 23.c5! bxc5 24.Bxc5, and the bishop would have been inviolate on account of WHITE having a back rank threat.

An 'uh, oh' moment...

How Black must have wished he'd castled betimes!

Black has no choice. Any other move incurs worse. At least this way he has a chance of holding an asymmetric end game.

The bishop pair is not to be sneezed at, neither.

I think the primary motive is to obviate back rank threats. E.g. 27.Rc1 would be no threat to the bishop as Black would simply dodge with the King (27...Kc6) and White would not have dared take the bishop. That the possibility of cutting the h6-bishop out of the game probably decided him which pawn to advance.

One has to bear in mind that although the defending side normally tries to avoid exchanges, especially of pieces, it is also in its interest to ensure they stay active. This is where the attacker has the advantage: to engineer situations in which the defender must accept exchanges OR a passive position. Most often the former is the lesser evil. Here, I think I would have kept the rooks on, and invite White to form a plan. I quite like 27...Be4, renewing latent back-rank threats.

No choice.

I like this spot for the bishop. If need be it can find safety on e6. It would be nice if the other bishop could be brought to c5, and the a-pawn advance to a5. Then, I believe, Black could snap his fingers at any scheme White might concoct. But that won't be so easy to arrange.