Daily Chess Puzzle

Today’s problem is from the World Championship match; a position I pondered and didn’t understand from the report of game 5 in Chessbase.com  and in particular Aryan Tari’s comments.

Since the start of 2018, I have decided to adopt the style of only saying 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

Aryan Tari’s annotations say that 18 d4 is a killer if 17..b3; but doesn’t even mention it after 17..Kd7.

Why?

Wby is it so strong after one move, but not even worth mentioning after another?

Caruana v Carlsen, game 5, London 15/11/18

Solution

The answer seems to be that by keeping the pawn on b4, hitting c3, White’s BSB has no square on which it is protected.

So 17..Kd7 18 d4 Ra8 hits the BSP; 19 Bb2 ed 20 cd Kc7:

and d5 isn’t a threat because the Bb2 is unprotected.

Contrast 17..b3 when after 18 d4 ed 19 cd the BSB can, if hit by Ra8, move safely to Bc3 from where the Nb1 protects it: so  d5 is threatened.

FEN

r7/1pPk1pbp/6p1/3bp3/1n2P3/5N2/3P1PPP/B3R1K1 w – – 0 21