Annotated chess game

Because when material down, exchange pawn but not pieces. If I can exchange all the pawns, and rooks come off I can sacrifice both bishops for the two extra pawns and he can't mate with king and two knights.

Overprotection can be useful, especially to stifle counter-play from an opponent reliant upon the activity of his pieces for counterplay and breaking down strong points. But White is so powerfully placed that overcaution can hold him back. 33.a5 looked a fine alternative, committing Black's defences to the Q-side. Even wholly so committed, they might not be enough.

Exchanging on f4 would have lost White no time, and left Black with the same problems and fewer resources to respond to them.

Interesting instance of how even late in the middle game, and with queens off the board, active pieces and a bind can compensate for a two pawn deficit. However, if and when White escapes the toils, the traffic is simply all one way.

Many thanks for your comments!