In the game which follows both players are trying to escort their pawns to the last rank but White appears to be coasting for a victory. However White blunders and makes things interesting with a checkmate in sight for Black. However, incredibly on the very next move, Black counter blunders and it is White who is sighting checkmate.

White: Viktor Korchnoi (2635) – Black: Alon Greenfeld (2570)
Beersheba, 1995
English Opening

1.c4 c5 2.Nf3 Nc6 3.d4 cxd4 4.Nxd4 Nf6 5.Nc3 e6 6.g3 Qb6 7.Ndb5 Ne5 8.Bf4
White plays a new move rather early in the opening. Other popular continuation is 8. Bg2 8.Bg2 a6 9.Qa4 Rb8
8...Nfg4 If 8...d6 9.Bg2 a6  10.Qa4 Bd7
9.e3 Qc6
This was not needed. Black had a better move in  9. ....a6 10.Nc7+ Qxc7 11.Qxg4 d6
10.h3  Wanting to drive back the knight and here this is an interesting move by White, tempting Black with a rook offer. If 10.e4 Bc5 11.Bxe5 Nxe5 12.f4 a6 13.fxe5 axb5 14.cxb5 Qc7
10...Nf3+  If 10...Qxh111.hxg4 Nf3+ 12.Ke2 e5 (12...Ng1+ 13.Kd2) 13.Nd6+ (13.Nc7+ Kd8 14.Nxa8 exf4 15.gxf4 b5)
11.Ke2 Nge5
If 11...e5 12.Qd5 12.b3 g5 Attempting to trap White’s dark bishop. If 12...a6 13.Bg2 axb5 14.Bxe5 Qc5 15.Bxf3 Qxe5 16.Nxb5 gives White better chances
13.Bg2  If 13.Bxe5 Nxe5 14.Bg2 Qxg2 15.Nc7+ Kd8 16.Nxa8 b6 and Black stands better
13...gxf4 14.exf4
More or less a forced move for if 14.gxf4 Rg8
14...a6 If 14...Qb6 15.fxe5 Nxe5 16.Na4 Qa5 15.fxe5 axb5 16.Bxf3 Qc5
A few interesting exchanges on both flanks of the board
17.Nxb5 Qxe5+ 18.Kf1 Bg7 19.Kg2

White has artificially castled If 19.a4 Qxa1 20.Qxa1 Bxa1 21.Nc7+ Kd8 22.Nxa8 Bd4 23.Ke2
19...Qxa1  If 19...Qb8 20.Nd6+ Ke7 21.c5 Bxa1 22.Qxa1 Rg8 23.Re1 Qa7 24.Nf5+ Kf8
20.Nc7+ Kd8 21.Qxa1
If 21.Nxa8 Qxa2 22.Nb6 Qa5 and White is distinctly better
21...Bxa1 22.Nxa8 Bd4 23.b4
If 23.Rd1 e5 24.a4
23...b6 24.Rd1 e5 25.a4 Rg8 26.c5
If 26.Rxd4 exd4 27.Nxb6 Re8 28.Kf1 d3 and things become a bit unclear
26...bxc5 27.b5 Rg6 28.b6 Rf6 29.Rb1 c4
If 29...Rxf3 30.Kxf3 Bb7+ 31.Ke2 Bxa8 32.b7 Bxb7 33.Rxb7
30.b7 Bxb7 31.Rxb7 d5 32.Rb8+
Worth a look is 32.Rb5
32...Kd7 33.Bg4+ Kc6 34.f4 c3
Black’s rook is awkwardly placed!
35.a5 c2

Diagram 1

36.a6 A terrible blunder! Black should have played 36.Nb6 Bxb6 37.axb6 Kc5  38.Rc8+ Rc6 39.b7 c1Q 40.b8Q Qd2+ 41.Kf1 Qc1+ 42.Kf2 Qd2+ 43.Be2 Qd4+ 44.Kf1 Qa1+ 45.Kg2
36...Bc5 Black now reciprocates the blunder. Black was simply winning after 36...Kc5 37.Bd7 Bc3 38.Rc8+ Kd4 39.Nc7 Rb6 40.a7 c1Q 41.Nb5+ Rxb5 42.Bxb5 Qb2+ 43.Kf3 Be1 44.Kg4 Qa3 45.a8Q Qxg3+ 46.Kf5 Qg6 checkmate
37.Rc8+ Kb5 38.Nc7+ Kc4 39.Be2+ Kb3 40.Ne6
If 40.a7 c1Q 41.a8Q Qg1+ 42.Kf3 Qf2+ 43.Kg4 Qxe2+ 44.Kh4 Rh6+ 45.Kg5 Qh5 checkmate
40...c1Q 41.Nxc5+ Ka3
If 41...Ka2 42.a7 Ra6 43.a8Q Rxa8 44.Rxa8+ Kb1 45.Ra1+ Kxa1 46.Nb3+
42.a7 Ra6 43.a8Q Rxa8 44.Rxa8+ Kb4 and Black resigned for White is threatening 45.Nd3+

Diagram 2

White to play and win
1.Qxh7+ Rxh7 2.Rg8 checkmate.