A positional mistake. 13.dxc5! was the only move in this position.

Fantastic move by Nepo. With this move, the Russian Super-GM guarantees safety for his king for the rest of the game.

Black is ready to throw hands at White's kingside.

White has almost completed development and has a good knight on e5, but the b-file cannot be occupied. How to continue?

With this move, White fixes the pawn on c6, which is attacked by the powerful knight on e5. Black can barely move here!

3...Nf6 4.h4 and White enjoys a fantastic space advantage!

The difference between bishops is significant. Once we have played e4, the b-file is accessible for our rooks, and the c4-pawn is very weak. Black can only await a slow death. It's very important to note that the bishop on d6 is controlling the b8-square so Black cannot fight for the open file!