One blunder can spoil the whole show

Chess Checks

Nothing can be more horrifying for a chess player than to agonisingly watch one single move bring about his downfall! There can be various excuses offered like lapse in concentration, oversight, miscalculation or simply time pressure.

The ensuing game is one where Black is struggling but does not look in danger of losing the game. However one blunder in the form of a knight move and his whole game collapses like a pack of cards on the very next move.

White: Milan Franic (2430) – Black: Juraj Nikolac (2435)
Pula, 1998
Queen’s Gambit Declined
1.d4  d5 2.c4 e6 3.Nc3 Nf6 4.Bg5. The Cambridge Springs variation
4. ..Nbd7 5.e3 c6 6.Nf3 Qa5 7.cxd5 Nxd5 8.Qd2 Bb4 9.Rc1 0–0.
Here Black can play 9. ..f6 or 9. ..e5
10.Bd3 Re8 If 10...e5 11.0–0 exd4   
11.0–0. If 11.e4 Nxc3 12.bxc3 Ba3  
11...e5. Black immediately pushes at the centre after White has castled
12.Qc2 h6 13.Bh4 Nxc3.
Black also has a choice of playing 13...exd4 14.exd4 (14.Nxd5 Qxd5 15.exd4 Qxa2) 14...N7b6 15.Ne5 Be6 16.Bh7+ Kh8 17.Bf5 Kg8 18.Bh7+ Kh8  
14.bxc3 Bd6 15.Bg3 Qc7 16.e4.
White decides that he wants to force things at the centre
16. ..exd4 If 16...c5 17.Bc4 b6 (17...exd4 18.cxd4 Bxg3 19.fxg3) 18.Qb3 Rf8 19.Nh4
17.cxd4 Bxg3 18.hxg3 If 18.fxg3 Nf6
18...Nf6 19.Rfe1 Qe7 20.Qc3 If 20.Qc5 Qxc5 21.Rxc5 Be6 22.Rb1 Re7 23.a4 Rd8
20...Be6 21.Bb1 Rad8 22.Ne5 Qd6 If 22...Ng4 23.Nxg4 Bxg4 24.f3 Be6 25.Red1 Qd6  
23.Rcd1
White can also think of 23.Nf3
23. ..Nd7 24.Nd3
White had a better move in 24.Nxd7 or even 24.Nf3 Bg4
24...Nf8 If 24...b6 25.e5 Qd5 26.Nf4 Qc4 27.Rc1 Qxc3 28.Rxc3 Nf8  
25.Nf4 Bg4 26.f3 Be6 27.Kh2 f6 28.e5
If 28.d5 cxd5 29.Nxd5 Qb8 with a balanced position  
28...fxe5 29.dxe5. If 29.Nxe6 Nxe6 30.Rxe5 Qxe5 31.dxe5 Rxd1  
29...Qxd1 Black gives up the queen for two rooks.
If 29...Qe7 30.Rxd8 Rxd8 31.Nxe6 Nxe6 32.Qc2 Nf8 33.f4
30.Rxd1 Rxd1 31.Bc2
If 31.Nxe6 Rxb1 32.Nc5 Ne6 33.Ne4 Rd1 34.f4 Rd7 35.Nd6
31...Rd7 32.Nxe6 Nxe6 33.Bg6
White could have strengthened his pawn structure with 33.f4
33. ..Ree7
If 33...Red8 34.Qb3 Re7 35.Qa3 c5 36.Qxa7 Nf8 37.Bc2 Rxe5 38.Qxb7
34.Qc4 Rd5
Once again better is 34...Rd4 35.Qc3 (35.Qe2 Rd5 36.f4 Nd4 37.Qh5 c5) 35...Rdd7 36.Qc4 Rd4  
35.f4  Kf8 36.f5 White decides to pile on the pressure
36. ..Nc5
If 36...Nd4 37.f6 gxf6 38.exf6 Re6  
37.f6 Rexe5 38.Qf4 Rh5+
If 38...h5 39.fxg7+ Kxg7 40.Qf7+ Kh6 41.Bc2 Ne4 42.Qf4+ Kg7 (42...Ng5 43.Qf6 checkmate) 43.Bxe4 and White is distinctly better
39.Bxh5 Rxh5+ 40.Kg1
Black has managed to maintain material balance but his pieces are far from being posted on good squares. The King is in danger and appears most vulnerable.  
Diagram 1
40...Ne6. A horrendous blunder! Black is lost after this move. He could have offered more resistance with 40...Kf7 41.fxg7+ Kxg7 42.Qd4+ (42.Qc7+ Kf6  43.Qd8+ Kf7 44.Qd6 Rg5 45.Qxh6 Ne6 46.Kf2 Rf5+ 47.Ke3 Re5+ 48.Kf3 Rf5+ 49.Kg4 Rg5+ 50.Kh4 c5)  42...Kh7 43.Qf6 Rd5 44.Qf7+ Kh8 45.g4 Rg5 46.a4 a5  
41.Qd6+ And it is all over for Black as 41.Qd6+ Kf7 42.Qe7+ Kg6 43.Qxe6 gxf6 44.Qg8+ Kf5 45.g4+  1–0
Diagram 2
White to play and win
 1.Qh4+ Kg8 2.Qg3+ Kh8 3.Bc3 Qxc3 4.Qxc3+ d4 5.Qxd4+ and White wins.