Pressure can induce errors at wrong time

Miscalculations and oversight can abruptly spell defeat in a game which has been going steadily in your favour. Most mistakes or blunders most often occur during the time controls when the players are under pressure to complete the stipulated moves (40 during the first time control).

In the game which follows, Black has a firm grip on the game and looks set to cruise to victory. However during the first time control he commits a terrible blunder, placing his queen on the wrong square, in all probability overlooking a stunning rook move.
White: Ulf Andersson (2630) – Black: Friso Nijboer (2475)

Ter Apel, 1996
Anti-King’s Indian System
1.d4 Nf6 2.Nf3 g6 3.g3 Bg7 4.Bg2 0–0 5.0–0 d6. If 5...d5 6.c4
6. Nc3. The King’s Indian Attack. White could have converted to the Queen’s Gambit by playing 6.c4
6...Nbd7. If 6...c6 7.e4 Nbd7 8.a4 Qc7 9.Re1 e5 10.h3 b6 11.Bg5 Bb7 12.Qd2 Rfe8
7.a4. White could have maintained balance with 7.e4 c5  8.e5 dxe5  9.dxe5 Ng4 10. e6

7...a6. Black played a new move here. If 7...a5 8.e4 e5 9.Re1
8.e4 e5 9.dxe5 dxe5 10.a5
White can play 10.Qe2 Qe7 11.Rd1 h6
10...b5. If 10...Qe7 11.b3 Rd8 12.Ba3
11. axb6 (en-passant) cxb6 12.Qe2 Bb7 13.Rd1 Qc7 14.Nd5
If 14.Nd2 .b5 15.Nf1 Rfc8 16.Ne3 Nb6
14...Nxd5 15.exd5 Rfe8 16.Ng5
If 16.c4 Rac8 17.Nd2 (17.b3 e4 18.Nd4 Nc5) 17...e4
16...h6 17.Ne4 f5 18.d6

White pushes his passed pawn and this might make things difficult for Black. If 18.Nc3 Qd6

18...Qc8 19.Nc3 e4
This is an interesting move! If 19...Bxg2 20.Kxg2 Qc6+ (20...e4 21.Nd5 And if 20...Qb7+ 21.Kg1) 21.Kg1 21...b5 22.Be3 f4 23.Bc1
20. Nd5. If (20.g4 Nf6 21.gxf5 gxf5 22.Bf4
20...Bxd5. Black should be more than happy to exchange the white bishop which was virtually out of play for White’s active knight

21. Rxd5 Qc6 22.Rd1
If 22.Qd1 Nf6 23.Rd4
22...Re6 23.c3. Better appears 23.f3 Nc5 24.fxe4 fxe4 25.Qc4 Kh7
23...b5. Strangely Black decides against grabbing the pawn with 23...Rxd6 24.Rxd6 Qxd6 25.Rxa6 Rxa6 26.Qxa6 Qd1+ 27.Qf1 Qc2 28.f3
24. Be3. If 24.f3 Rae8 25.fxe4 fxe4  25.Bf4 g5 And if 24.Bf4 g5 25.Be3 Rxd6 26.Rxd6 Qxd6 27.g4 f4 28.Bxe4 Re8 29.Rd1 Qe7 30.Bc6 with an equal position
24...Rxd6.

He does capture the pawn finally!

25.Rxd6 Qxd6 26.Rd1 Qe6 27.Qd2
White can look at 27.f3 Re8 28.Re1 exf3
27...Ne5 28.Bxh6 Nc4 29.Qg5
If 29.Qc1 29...Nxb2 30.Bxg7 Nxd1 31.Bd4 e3 32.fxe3 Rd8 33.Qxd1 Qxe3+ 34.Bxe3 Rxd1+ 35.Kf2

29...Bxh6. If 29...Nxb2 30.Rd8+ Rxd8 31.Qxd8+ Kh7 32.Bxg7 Kxg7 33.Bf1 Nd3 34.Bxd3 exd3

30. Qxh6. Black looks better now!

30...Nxb2 31.Rd4 Nc4 32.g4

If 32.f3 e3 33.Rh4 Kf7

32...Rf8. The correct move here was 32. ..Re8 33.Kh1 Ne5 34.gxf5 gxf5
33. gxf5 Qxf5 34.Rxe4 Qxf2+ 35.Kh1 Qf6. This is a big blunder! Black could have hung onto his advantage with 35...Qf5 36.h3 Qh5 37.Qxh5 gxh5 38.Re6 a5 39.Bd5 Kg7 40.Bxc4 bxc4 41.Ra6 Rf5 42.Kg2

Diagram 1

36. Rf4. A lethal move which in all probability Black would have missed in his calculation

36. ..Qxf4. If 36...Qg7 37.Bd5+
37.Bd5+ Qf7
If 37...Rf7 38.Qxf4
38. Qxg6+ 1–0
Diagram 2
White to play and win
1.      Bc4+ Qxc4 2.Qe8+ Nxe8 3.Rf8 checkmate.