White has now a piece for a pawn, and Black has no positional compensation for it. Moreover, the unforced exchanges of Black's bishops and QN leave Black with very meagre resources to mount a defence, much less any sort of counter-attack. Without minor pieces, Black's blocked pawn position hampers his remaining rooks' mobility.
15... Qd8c7
Black clears the back rank to centralize his rooks.
16. Qe1e3
The absence of White's dark-squared B must be compensated, so the Q now covers the dark squares.
16... Rf8e8 17. Rf1e1 a6
Telegraphing Black's intention to move the QR.
18. Bg2f3
Since the long diagonal is closed, the B must be manoeuvred to a better place; Bf3 prepares to bring the B over to the b1-h7 diagonal eventually. Because the files are closed, the game strategy will be to play for control of diagonals.
18... Ra8d8 19. Ne5g4 Nf6xg4
This trade favours White in several ways. First, every exchange tends to magnify White's material advantage; second, the removal of Black's KN leaves the Black K without defenders; third, the N will be retaken with the h3 pawn, opening a potential attack-file to the Black K; finally, this was the last piece Black had which could manoeuvre outside the locked pawn structure. However, the alternatives, 19. ... Nd7 or Nh7 would have been met by 20. Nxh6+, g7xNh6; 21. Qxh6, leaving the Black K very exposed.
20. hxg4 Qc7e7
Black must prevent g4-g5, breaking open the Black K position, hence ... Qe7, holding the g5 square.
21. d4
This fixes the Black centre pawns and opens the b1-h7 diagonal for eventual possession by the White KB. The Black pawn structure is mostly on White squares, which hampers the White KB, but it also locks in Black's own rooks. Black, without any minor pieces, is effectively imprisoned by his own pawn structure. White, on the other hand, has two half-open files for his rooks: the e-file and h-file, and 2 promising diagonals: b1-h7 and c1-h6.
21... g5
Unpleasant, but what else to do? White was threatening to play Kg2, double the rooks on the h-file, sacrifice one of them on h6, and crash through with a combined Q and R on h6. The text move creates space for Black to get the K to g7 and defend the h-pawn by means of Rh8, while preventing White's break g4-g5. However, it seriously weakens b1-h7 diagonal.
22. Kg1g2 Kg8g7
Immediate disaster is averted: Black has just enough time to get his KR back to h8 if White tries Rh1, Rh5, and Ra1-h1.
