The 4NCL Online event launched last month, and the first round Henry Li, playing board 1 for the Gonzaga B team (“Gonzaga B Sharps”), had White against Simon Williams.
The game reached a rook ending in which Black was two pawns to the good, but Williams misplayed it, simplifying to a R + 2P versus R ending, but one of the exceptional ones that is drawn.
The critical moment came a few moves later:
60. ?
After the game’s 60. Rd2?, White was lost, and Williams duly converted.
White has exactly one move that draws: 60. Ra4!. The point is that 60… b5 61. Ra6! cuts the black king off, and the black rook can’t both keep the white king cut off and support the pawn. Similarly, 60… Kc6 61. Kd4! Kb5 62. Ra2! prevents Black from making any further progress.
These days, it is easiest to explore the possibilities via the online Nalimov endgame tablebases. In former times, standard manuals would have to be consulted. The situation after 60. Ra4 b5 61. Ra6 is explored in Reuben Fine’s Basic Chess Endings (David McKay, 1941), pp. 294-6. In such cases, the defending king must be cut off four files from a knight’s pawn for the position to be a win. The critical position (W: Kb2, Re1, b4; B: Kf5, Rh3) was analysed by Grigorieff in 1937: White to play wins, Black to play draws.