15.Ne5
Active play! White immediately seizes the opportunity to return to e5.

And White was a pawn up. Sometimes chess seems simple, and Karjakin went on to win this important game.

Alexander Alekhine, the fourth World Champion, was born on this day in 1892.
He ascended to the throne in 1927 by defeating his predecessor, Jose Raul Capablanca, and held the title until his death in 1946, with a short interruption between 1935-1937 (when Max Euwe reigned).

Black has just retreated his knight from b4 and White now seized his chance:

In three moves, including the exchange sac, White has established a superb knight on d5 : a perfect post from which to target Black's weakened kingside. White has ample compensation and is clearly better, even close to winning.

White has regained his material with simple moves. The bishop on f6 is not in any way worse than any of the black rooks and it will clearly support the advance of the passed h-pawn. White won shortly.

"Modern Chess is too much concerned with things like pawn structure. Forget it, checkmate ends the game!"
Nigel Short

With a kingside pawn structure characterized by the move h2-h3 ( ... h7-h6), you should beware of a quick opening of lines (for example, after opposite-side castling, by an advance of the opponent's g pawn) or certain straightforward tactical motifs. For now, we will look into another pattern: a long-term sac on h3 /h6!

In this position Vachier-Lagrave was taken by surprise:

You would expect such a bishop sac to be followed up with a rook check on the g-file or at least the queen sortie to h4. Neither is possible here, yet after this quiet queen move White is unable to defend h3 as 17.Kg2 is met by 17...Nf4+, while 17.Kh2 is illegal!

White wants his queen to join the defence.