35. RxP Kt-R6ch 36. K-R1 P-Kt5 37. R-Q7 Q-K4!!
If QxQ, Black mates in three.
38. R-Q8ch RxR 39. RxRch K-R2 40. R-Q1 QxQch
Curiously enough there is nothing better. Q-B2 only leads to the exchange of Queens and the same end-game, which, however, is an easy win for Black, as the permanent mating threat keeps the White Rook tied to the first rank, whilst the Black King threatens to capture all the White pawns.
If Q-B2 White forces the exchange of Queens with the following combination: 41. Q-Q2, R-B7; 42. Q-Q3, R-B8ch; 43. K-Kt2, with a threat of Kt-B6ch and Q-R7 mate. Black therefore would have to play Q-B7ch, etc., as in the game.
41. KxQ R-B7ch 42. K-R1 RxP 43. R-R1 P-Kt4 44. Kt-B6ch K-Kt2 45. Kt-K4 K-Kt3 46. Kt-Q6 P-QR4
We have now a position with a forced move. If the White Knight moves, there follows K-B4-B5, etc. Therefore White gives up his R P voluntarily.
47. R-QB1 RxP 48. Kt-B4 Kt-Kt4
Now Kt-B6 and RxP mate are threatened.
49. Kt-K5ch K-Kt2 50. Kt-Kt4 R-K7 51. R-B5 R-K8ch 52. K-Kt2 Kt-R6 53. R-B7ch K-B1 54. R-B1 R-K7ch 55. K-R1 Kt-B7ch 56. K-Kt1 Kt-R6ch