📗12...Nb4! Black voluntarily give up a pawn to secure light squares for himself.
📗19...Qd7 Black dominates light squares and white's pawn barely could be pushed. Nevertheless, a pawn is a pawn. White does not have advantage but black should be careful not giving white further initiative.
📗21.Rc1! this keeps the game going. In a rapid, Karjakin calculates likes a beast!
📗23...Bxf3?! Absolutely unnecessary! This is the only way white can manage to push his d-pawn! Smirnov should have just stayed still and enjoy looking at his nicely placed pieces! Although the move is actually the best move according to the engines, the practical complications in a rapid does not worth entering this line!
📗9.Bd2!? An interesting and new idea. The point of this move is development without getting on the way of white's other pieces.