White is helpless against the two powerful Bishops.
16. R-K1ch K-B1
Black forfeits his chance of castling, not a great loss under the circumstances. In any case his KR is needed on the Rook’s file, and Black would only have castled on the Queen’s side if at all.
17. Q-B3
Here P-KR3 was essential in order to prevent the further advance of the KRP. The weakness at Kt3 would not have been so serious in the absence of a Black Knight. Now Black forces the advance of White’s KKtP, and the Bishops become immediately effective.
17. … P-R6 18. P-KKt3
not P-KKt4 on account of Q-R5.
18. … Q-Q2 19. B-Q2 B-Kt5 20. Q-B1
If Q-Q3, Black plays Q-B4 and White cannot exchange Queens because of B-B6 mate.