Knight endgame misplayed

The diagram shows the position after White's 62nd move. This is still an 8-man ending, not solvable directly by tablebases, but it should be evident that Black's defence hinges on exchanging one pair of pawns, after which he can sacrifice his knight for the last White pawn. So an active 62nd move would have brought about a simplified ending but some variations were tricky.

Alternatively Black could have defended passively, but in practice he fell between these two stools and grandmaster Nikolic found a way to win - an important step on the way to becoming champion.

Predrag Nikolic - Bernardo Roselli Mailhe
World Senior Championship 50+, 2015

1.Nf3 Nf6 2.c4 e6 3.g3 d5 4.Bg2 Be7 5.0-0 0-0 6.d4 b6 7.cxd5 exd5 8.Nc3 Bb7 9.Bf4 a6 10.Rc1 Nbd7 11.Ne5 Bd6 12.Nd3 Qe7 13.Qb3 Bxf4 14.Nxf4 c6 15.Rfe1 Ne4 16.Bh3 f5 17.Ncxd5 cxd5 18.Rc7 Nd6 19.e4 Kh8 20.e5 Rac8 21.Rxc8 Nxc8 22.Rc1 Nb8 23.Nxd5 Qd7 24.Bg2 Nc6 25.Qe3 Re8 26.Nf4 b5 27.Nd3 Ba8 28.d5 Na5 29.e6 Qe7 30.b3 Nb7 31.Ne5 Nbd6 32.Qc5 Bb7 33.f4 Kg8 34.h4 Ne4 35.Bxe4 Qxc5+ 36.Rxc5 fxe4 37.Nf7 e3 38.Kf1 Bxd5 39.Rxd5 Rxe6 40.Ne5 Nd6 41.Ke2 h5 42.Kxe3 Nf5+ 43.Kf3 Rd6 44.Rxd6 Nxd6 45.Nc6 Kf7 46.g4 hxg4+ 47.Kxg4 Kf6 48.Kf3 Kg6 49.b4 Nc4 50.Ke4 Kh5 51.Ne5 Nb6 52.Nf3 Na4 53.Kd3 Kg4 54.Nd4 g6 55.f5 gxf5 56.h5 Kxh5 57.Nxf5 Kg5 58.Nd6 Kf6 59.Ne8+ Ke5 60.Nc7 Nb2+ 61.Kc2 Nc4 62.Kc3

62...Ke4?? [62...a5!! reduces material by force, although 63.Kb3! is a bit tricky and probably the line Black failed to calculate: (63.bxa5 Nxa5 64.Nxb5 (or Kb4) 64...Nb7 and the knight will always be able to sacrifice itself for the a-pawn when it advances.; 63.a3 axb4+ 64.axb4 (64.Kxb4 Nxa3= ) Black can draw in several ways but the simplest is 64...Nb6 65.Nxb5 Nd5+ and 66...Nxb4.; 63.Nxb5 Nd6 and whatever White plays, the reply will be 64...axb4+ reducing to an a-pawn which will never win, with or without knights on the board. (Also 63...Ne3 holds, somewhat surprisingly.)) 63...axb4 (63...a4+? 64.Kc3 Nd6 65.Kd3 is zugzwang as the White king gains entry to d4 with winning chances,) 64.Kxb4 (64.Nxb5 ) 64...Nb6 65.Kxb5 Nc8 (Not 65...Nd5?? 66.Nxd5! If the N moves elsewhere then ...Nc3+ and ...Nxa2. 66...Kxd5 67.a4 Kd6 68.Kb6 (68.a5?? Kc7 and the K reaches a8.) 68...Kd7 69.Kb7+- ; 65...Nd7 also draws.) 66.Kc6 and with care Black can draw; the tablebase indicates three moves. (66.a4 Kd6 ) 66...Kd4 This line depends on precise calculation with forced moves: (66...Ne7+ ; 66...Nd6 ) 67.a4 Black is now committed to chasing the pawn from behind: 67...Kc4! 68.a5 Kb4! 69.a6 Ka5! 70.Kb7 Nd6+ 71.Kc6 (71.Ka7 Nc8+ with perpetual check as White cannot allow ...Kb6.) 71...Nb5! bringing the game to an immediate end 72.Nxb5 Kxa6 Q.E.D. In the actual game, Black tries the king march from behind but overlooks that the absence of his king from the battlefield means White can sacrifice the knight.; 62...Kd6 with any sensible follow-up would draw, despite the loss of the a-pawn, e.g. 63.Nxa6 Kc6 64.Nc5 Nb6 with a blockade strategy.] 63.Nxa6 The tablebase says White mates in 32 moves. 63...Nd6 64.Nc7 Ke3 65.Nxb5! Nxb5+ 66.Kc4 Nd6+ 67.Kd5 Nc8 68.Kc5 Kd3 69.b5 Kc3 70.a4 Ne7 71.a5 1-0

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