Knight versus RPs

The position in the first diagram here arose after White's 51 Kxh6.

That inaugurated a seven-man ending in which Black has knight and pawn against three White pawns. It illustrates the difficulties that a knight can have against passed RPs and here White has two of them. Black has already missed a winning line. He had hastily queened his f-pawn in order to win White's last minor piece, but he should first have advanced it to h5 where his knight could have protected it.

The Houdini analysis engine tends to think Black is still winning but the Lomonosov tablebase shows it is a draw with correct play.

The second diagram shows the position after Black's move 60...Ng3-f5??, which turned a drawn ending into a win for White. This change of assessment occurred because the knight released its blockade of the h-pawn, after which the h-pawn was able to advance one square further.
Now the two rooks' pawns became too strong for the knight to cope. On its own, it could restrain the h-pawn but never capture it. The black king had to fulfil two tasks (guard his c-pawn and stop the a-pawn) which it could not do without the assistance of the knight.
Even so, White later made a slip which should have allowed a draw after all, but Black immediately went wrong again.

Keegan O'Mahoney - FM Mikhail Popov

Albin Counter-Gambit [D08]
FIDE World Junior Championship (12.28), 14.09.2015

1.d4 d5 2.c4 e5 3.dxe5 d4 4.Nf3 Nc6 5.a3 a5 6.e3 Bc5 7.exd4 Nxd4 8.Be3 Bg4 9.Be2 Nxf3+ 10.Bxf3 Qxd1+ 11.Bxd1 Bxe3 12.Bxg4 Bd4 13.Nc3 Bxe5 14.0-0-0 Nf6 15.Bf3 Bxc3 16.bxc3 0-0 17.Bxb7 Rab8 18.Bf3 Rb3 19.Kc2 Rfb8 20.Rb1 Rxb1 21.Rxb1 Rxb1 22.Kxb1 Nd7 23.Kc2 Nc5 24.Kd2 Kf8 25.Ke3 Ke7 26.Kd4 Kd6 27.Bd5 f6 28.Bg8 h6 29.f4 g5 30.g3 gxf4 31.gxf4 Na4 32.Bf7 f5 33.Be8? [33.Bd5 to get B working on both wings 33...Nc5 (33...c6 34.Bf7 c5+ 35.Kd3 ) 34.Bf3 (34.Bg2 ) ] 33...c5+ 34.Kd3 Nb2+ 35.Kc2 Nxc4 36.Kb3 Ne3 37.Ka4 Nd5 38.Kxa5 Nxf4 39.Kb5 Nd5 40.Kc4 Nf6 41.Ba4? [41.Bb5 should be fairly comfortably tenable.] 41...Ng4 42.h3 Nf2 43.h4 f4 44.Bc2? [44.Bb5= ] 44...Ng4 45.Kd3 f3 46.Ke4? K should remain in square of passed pawn. [46.Ba4 ] 46...f2-+ 47.Bd3 Nh2 48.Kf5 48...f1Q+? Gives White excellent drawing chances [48...Kd5 /\49.Kg6 Nf3 (49...Ng4!? ) 50.Kxh6 Nd2 51.a4 c4 52.Be2 Ke4 53.a5 Ke3 54.a6 Kxe2 55.a7 f1Q 56.a8Q Qf6+ 57.Kh5 Qxc3-+ ; 48...h5 /\49.a4 f1Q+ 50.Bxf1 Nxf1 51.Kg5 Ng3 52.c4 Kc7 53.Kf4 Nf1 54.Kg5 Ne3 55.Kxh5 Nxc4 ] 49.Bxf1 Nxf1 50.Kg6 Kc6 [50...c4 51.Kxh6 7-man ending. Houdini tends to think Black is winning but tablebase shows it is a draw. 51...Kc6 (51...Ng3 is one of Houdini's tries 52.a4 (52.Kg6 also holds) 52...Ke7 53.a5 one of several moves to draw) 52.Kg6 Ng3 53.Kg5 looks the most natural of the moves which draw, though it allows a N fork: (53.h5? loses 53...Nxh5 54.Kxh5 Kb5 and WK is too far away; 53.a4 seems to help Black but does not lose 53...Kb6 54.Kf6 Ka5 55.Ke5 These moves are not the only ones to hold but Houdini persists in saying -+ 55...Kxa4 56.Kf4! This is an only move 56...Ne2+ (56...Nh5+ 57.Kg5 Ng3 58.Kf4 repeats) 57.Ke5! Nxc3 58.h5! Now Houdini sees it cannot stop White queening. A drawn ending of Q+N v Q arises.) 53...Ne4+ 54.Kf4 Nxc3 55.Ke3[] Threat Kd4 to win Black's pawn 55...Kd5 56.h5[] Ke5 57.h6 Kf6 58.Kd4= ; 50...Ng3 51.Kxh6 c4 transposes] 51.Kxh6 This should be a draw. A knight can have problems against passed RPs and here there are two of them. Black probably believed he could win, though, because he still has a pawn, and this was ultimately his downfall. 51...Kb5 [51...c4 was Houdini's idea, claiming two and a half pawn advantage for Black, because it fails to reset the assessment to zero when the last Black pawn is captured. White draws in fact: 52.Kg5 This looks sensible but many moves hold. 52...Ng3 The only good move for Black says Houdini. 53.Kf4 This is OK although it allows a fork. (White could also play some other moves and draw.) 53...Ne2+ 54.Ke3 Nxc3 55.Kd4 and the last pawn falls. 55...Nb5+ 56.Kxc4 Nxa3+ Black can stop the h-pawn.] 52.Kg5 Ng3 53.Kf4 Ne2+ 54.Ke5 Ng3 55.Kd5 Ne2 56.c4+ Kb6 57.Kd6 Ng3 58.Kd7 Ne4 59.Ke6 Ng3 60.Kd5 60...Nf5?? The losing move; the tablebase says White can mate in 39 moves. [60...Nh5 blockades the pawn and holds.; 60...Ne2 is also sufficient to draw, since 61.h5?? would lose to 61...Nf4+ and ...Nxh5.] 61.h5 Ne3+ 62.Ke6 Also Ke5 and Kd6 win according to the tablebase. 62...Ng4 63.Kd6 Best according to the tablebase which says White mates in 37 moves in the longest lines (63...Nh6 or 63...Ne3). See note to move 65. 63...Ne3 Else the Black c-pawn is lost or the h-pawn advances. [The main line after 63...Nh6 goes 64.a4 Nf5+ 65.Ke5 Ne3 66.Kf6 Ng4+ 67.Kg5! Ne5 68.Kf5 Nf7 69.Ke6 Nh6 70.Kd5 Ng8 71.a5+ Ka6 72.Kd6 Kxa5 73.Kxc5 and White wins as in the game, because of the widely separated pawns and the defending king cut off.] 64.Ke6 Although White cannot defend the c4-pawn he is still winning thanks to the strong h-pawn. 64 a4! is the quickest (mate in 36), while the text move or 64 Kd7, Ke5 or Ke7 do not spoil the win as White can return to the position and play a4. 64...Ng4 [64...Nxc4 65.h6 and soon promotes.] 65.a4?? This advance should only be played when the white king is in contact with Black's pawn. Here it jeopardises the win but Black did not notice and made the "natural" reply, after which White found the correct plan and won. [65.Kd6 repeats the position at move 63, after which he is ready to advance a3-a4.] 65...Ka5?? Two moves would have drawn here. [65...Kc6 66.Kf5 Nh6+! (Everything else loses.) 67.Kg6 Ng4 or 67...Ng8. White can never win the knight but equally Black has insufficient time to go for the a-pawn.; 65...Kc7 since if 66.Kd5 Nf6+ 67.Kxc5 Nxh5= ] 66.Kd6[] [66.Kd5 only draws: 66...Nf6+ 67.Kxc5 Nxh5 68.Kd5 Nf4+ ] 66...Kb4 [66...Kxa4 67.Kxc5 Ka5 68.Kc6 and with BK "offside" the N is unable to cope with both pawns. 68...Ne5+ (68...Kb4 69.c5 Kc4 (69...Nf6 70.h6 ) 70.Kd6 Nf6 71.c6 (71.h6 also wins.) 71...Ne8+ 72.Kd7 Nf6+ 73.Kd8 Nd5 74.h6 etc.) 69.Kd6 Even Kc7 would win. Black cannot take the pawn in either case. 69...Nf7+ (69...Nxc4+ 70.Ke6 and ther h-pawn cannot be stopped.) 70.Kc5+- Perhaps surprisingly, this move which blocks the c-pawn is the quickest win because it restricts Black's K.] 67.a5! Best, although 67 Kc6 also wins. 67...Ne3 [67...Kxa5 68.Kxc5 wins as in the 66...Kxa4 line. Although it's Black's move, this does not save him. 68...Ka6 69.Kc6! Ka7 (69...Ne5+ 70.Kd6 Or Kc5 or Kc7, for if 70...Nxc4+ 71.Ke6 Nd2 72.h6 Ne4 73.Kf5! ) 70.Kc7! ] 68.a6 Nxc4+ 69.Ke6 Kb5 70.a7 Nb6 71.h6 Black could resign 71...Ka6 72.h7 Kxa7 73.h8Q Ka6 74.Kd6 c4 75.Kc5 c3 76.Qh6 1-0

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