Giri - Nepomniachtchi: fortress or not?
Ian Nepomniachtchi © FIDE / Lennart Ootes

Giri - Nepomniachtchi: fortress or not?

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In the game between Anish Giri and Ian Nepomniachtchi at the FIDE Candidates, the players reached the following position after 48.... Qxa2:

Anish Giri - Ian Nepomniachtchi after 48... Qxa2

Does White have a fortress or not? Let's have a look at some relevant endgame theory.

Salvioli showed in 1896 that the following position is a draw with the white king on e2 and winning for Black with the white king on g2.

Salvioli, 1896 - draw with the white king on e2
Salvioli, 1896 - win with the white king on g2
Mark Dvoretsky explains in Dvoretsky's endgame manual:
1. An important technique of exploiting an advantage can be a queen sacrifice that results in a winning pawn endgame.
2. The weaker side should keep his king in front of the opponent's pawn; this can often (but by no means always!) neutralize the threat of the queen sacrifice.
3. With the black king on the 2nd rank, White's position is most often lost.
Dvoretsky shows the following study from Dedrle, 1925:
F. Dedrle, 1925 White to move wins
White wins by preventing Black to go to g7 and subsequently sacrificing his queen for the rook converting into a winning pawn endgame.
F. Dedrle, 1925 Black to move draws
This all seems easy but is not trivial. The position below is from Saemisch - Prins, Hastings 1938/39. Saemisch offered a draw in this position not knowing that he had an easily winning position by preventing the black king to come to g7. Keres showed that this position could be won using the Dedrle's analysis above,
Saemisch - Prins, Hastings 1938/39: analysis by Keres
Let's return with this knowledge to the game of Anish Giri and Ian Nepomniachtchi
Position after 48... Qxa2
We now know that this endgame is winning for Black if White did not have an h-pawn. The White king is on g2 and can not get to e1 or e2. Does the h-pawn make a difference? Let's see what happened in the game:
The winning plan for Black was to force White to give up the g-file. Subsequently, the Black king crossed the g-file to take the h4-pawn and then returned to d4 and win the subsequent endgame by sacrificing the queen for the White rook or by infiltrating with the king to d2 by playing Kd4-c3-d2.
Finally, please note that the position of the h-pawn does matter.
Let's look at the analysis position with the pawn on h3 instead of h4.
Anish Giri - Ian Nepomniachtchi (pawn on h3 instead of h4)
This position is a draw as the Black king does not have access to g4 because of pawn h3 and Black can not sac his queen for the rook and obtain a winning pawn endgame without winning h3. Imagine that Black tries to achieve the following position: 
White to Move
White can play here 1.Re3 as after 1... Qxe3 2.fxe3 Kxe3 3.h4 the pawn race is a draw.