Daily Chess Puzzle

Today’s position is a snippet from the recent Grenke Open.

As is my custom, I only say which side is to play: and not giving an idea if the move wins or otherwise, unless on occasion I think signposting would be helpful. Instead, the problems are posed with the instruction to decide what you would play, as in a game.

Black to play

Svidler v Carlsen 28/4/19

Solution

Whilst not at all a “to play and win” or even “to play and be better”, I watched the start of this game live, and was astounded that Magnus played 1…ab here.

I had assumed 1…Qb6, to keep the pawn structure intact.

My engine, like Magnus, prefers 1…ab.

I wonder why: perhaps readers can offer explanations? My guesses are around (i) opening of the a-file for the Ra8; (ii) defending of the Pc5, thereby looking to a future d6-d5.

Views welcome, in the comments box.

FEN

r1bqk2r/pp2bppp/1Nnp4/2p1p3/2B1P3/3P4/PPP2PPP/R1BQKN1R b KQkq – 0 9