Every Every move in a game of chess is crucial and has to be executed after careful consideration and calculation. It is very important not to waste moves (making moves which have to be taken back without having any effect on the position). Such a move is called a ‘tempo’ lost and a ‘tempo’ gain for the opponent.
In the game which follows, there are no fireworks till the mid-way stages but then Black makes a mistake on the 18th turn with a queen move. This results in the loss of two moves or tempi and eventually black ends on the losing side.
White: Robert Tibensky (2425) – Black: Hrvoje Stevic (2395)
Piestany, 1996
Trompowsky Opening
1.d4 Nf6 2.Bg5
The Trompowsky Opening
2. ..c5
If 2...Ne4 3.Bf4 c5 4.d5 Qb6 5.Bc1
3.d5 Qb6 4.Nc3 h6
If 4...Qxb2 5.Bd2 Qb6 6.e4 e5 7.f4 d6 8.Rb1 Qd8 9.Nf3 exf4 10.Bxf4 Nh5 11.Bd2 g6 12.Bb5+ Nd7 13.e5 dxe5
5.Bc1
Playing a novelty here . If 5.Bxf6 Qxf6 6.e4 a6 7.a4 d6 8.Nf3 Nd7 9.a5 g5 10.Be2 Bg7 11.0–0 h5
5...d6 6.e4 g6 7.Be2 Bg7 8.Nf3 0–0
If 8...Bg4 9.0–0 Bxf3 10.Bxf3 0–0 11.a4
9.Nd2
Interesting move
9. .. Qd8 10.a4 e5
Black decides to transpose into a King's Indian type pawn-structure but white looks better here. If 10...e6 11.Nc4 exd5 12.exd5 Bf5 13.Bf4 Ne8 14.Qd2
11.Nc4 Ne8
Taking a new start
12.0–0
Taking his King to safety. White is enjoying space advantage and in all possibility will go for an attack
12...Nd7
If 12...f5 13.exf5 gxf5 14.f4 e4
13.f4. Here 13.g3 looks a better option
13...exf4 14.Bxf4 Ne5
If 14...Qe7 15.Qd2 Kh7 16.Rf2
15.Qd2
If 15.Nxe5 Bxe5 16.Bxe5 (16.Bxh6 Qh4) 16...dxe5  with the idea Nd6
Would have Black, blockading the Black squares which should work in his favour
15...Kh7
There was no need to actually waste a move here. Black could have instead played 15...Nxc4 16.Bxc4 g5!? 17.Bg3 f5
16.Kh1
White also takes time off. If 16.Nxe5 Bxe5 (16...dxe5 17.Be3 b6 18.a5) 17.Bxh6 Bxh2+ 18.Kxh2 Qh4+ 19.Kg1 Qxh6 20.Qxh6+ Kxh6 21.Bb5 Kg7 22.Bxe8 Rxe8 23.Rf4 Bd7 24.Raf1 f5
16...b6 17.Rf2 a6 18.Raf1
18. ..Qc7
Not exactly the right continuation as Black loses two moves (Tempo) and allows White to whip up an attack. Black could have tried 18...Ng4 19.Bxg4 Bxg4
19.Ne3
Changing direction!
19. .. Ra7 20.h3 Qd8 21.g4
White gets into aggressive mode and rightly uses his pawn pushes  to weaken Black’s king side
21...Re7
If 21...Bf6 22.Bxh6 Kxh6 23.Rxf6
22.h4 Nf6
Worth a look was 22...Nd7
23.Rg1 Nfd7
Better for Black would have been 23...Rh8 with the dies Kg8 and Nfd7 . This knight exerted control on the crucial central e5 square.
Now White gets a good opportunity
24.g5 h5 25.Nf5
A more or less routine like knight sacrifice to shatter the King-side.
25...gxf5
Black has no choice. He is forced to accept the knight else his vital d6 pawn falls.
26.exf5 Rh8
Black should have played 26...f6  27.g6+ Kg8 28.Bxh5 Nc4 29.Qc1 Nde5 30.Bg3 with White in a dominating position
27.f6 Ree8
White gets back his piece with interest in the form of a ruptured King side. If 27...Nxf6 28.gxf6 Bxf6 29.Qd3+ Ng6 30.Bxh5
28.fxg7 Kxg7 29.Rgf1 Ng4
If 29...Re7 30.Ne4 Ng4 31.Nxd6! Nxf2+ 32.Rxf2
30.Bxg4 hxg4 31.Bg3 Re7
If 31...Ne5 32.Bxe5+ dxe5 33.Rxf7+ Kg8 34.Qf2 Rh5 35.Ne4 Qxd5 36.Rf8
32.Bxd6 Rxh4+ 33.Rh2 Rxh2+ 34.Qxh2 Re3 35.Rxf7+ and Black resigned as he cannot avoid check-mate after 35. .. Kxf7 36.Qh7+ Ke8 37.Qg6 check-mate.
Diagram 2
White to play and win
1.Rxe5+ Kxe5 2.Bf4+ Ke6 3.Re1+ Kd7 4.Bf5+  and White wins.