One has to be aware of time control

Apart from chess skills on the chessboard, one has to be totally aware of the time control and make the mandatory moves in the stipulated time. The first time control is for 40 moves and over the years there have been many amendments starting with two and half hours each for the first forty moves, to two hours and then one and half hour. A player loses the game if he does not make the stipulated moves in the allotted time.

In complicated positions players often blunder in time shortage or do not complete the moves. However there are times when a player makes a mistake and is under the illusion that he has completed the moves when he is actually short, of a move or two. The ensuing game is one such example where Black oversteps the first time control, falling short by one move in a position which could have ended in a draw.
White: Boris  Alterman (2615) – Black: Roman Slobodjan (2535)
Bundesliga  Germany , 1999

Slav Defence

1.d4 d5 2.c4 c6 3.Nf3 Nf6 4.e3 Bf5 5.Nc3 e6 6.Nh4 Be4
Here better appears 6. ..Bg4 or 6. ..Bg6
7.f3 Bg6 8.Qb3 Qb6
Inviting an early exchange of queens If 8...Qc7 9.Nxg6 hxg6 10.f4 Nbd7 11.Be2 Bd6 12.Bd2 dxc
9.Nxg6
If 9.Bd2 Nbd7 10.0–0–0 Be7 11.Be2 Rc8 12.Nxg6 hxg6 13.Kb1 Qxb3 14.axb3 a6
9...hxg6
If 9...fxg6 10.g3 Nbd7 11.Bd2 Bd6 12.Kf2 Qc7 13.f4
10.Bd2
If 10.c5 Qc7 11.e4 dxe4 12.fxe4 Nbd7
10...Nbd7
If 10...Bd6 11.0–0–0 Qxb3 12.axb3 Rxh2 13.Rxh2 Bxh2
11.Be2 Bd6 12.f4
If 12.0–0–0 Qxb3 13.axb3 Bxh2 14.e4 dxe4 15.fxe4 e5
12...Rc8
If 12...Qxb3 13.axb3 Bb4 14.0–0
13.0–0 Qxb3
Black no exchanges queens. If 13...0–0 14.Rad1 c5 15.Qxb6 Nxb6 16.cxd5 Nbxd5
14.axb3 a6 15.Bf3
If 15.Bd3 c5 16.cxd5 exd5
15...Bb8
Difficult to understand this retreat. He could have played 15. ..Bb4
16.g4 Nb6 17.g5
Too much aggression! He  could have played 17.c5 And if 17.Be2 c5 (17...Ne4 18.Nxe4 dxe4 19.Kg2 f5 20.h3) 18.g5
17...Ng8
If 17...Nfd7 18.c5 Na8 19.e4 dxe4 20.Nxe4
18.cxd5
If 18.e4 dxe4 19.Bxe4 Ne7
18...cxd5
If 18...exd5 19.e4 (19.Na4 Nxa4 20.bxa4 Ne7) 19...dxe4 20.Nxe4
19.e4 Ne7 20.exd5 Nbxd5 21.Nxd5 Nxd5 22.Bxd5 exd5 23.Ra5
If 23.Rfe1+ Kd7 24.Ra5 Ba7
23...Rc2. Invading the seventh rank. If 23...Rh3 24.Re1+
24.Rxd5 0–0 25.Bc3 Re8 26.Rf2
If 26.Rf3 f6 (26...Rc1+ 27.Kg2 Rc2+ 28.Kg3) 27.gxf6 gxf6 28.Rd7 g5 29.fxg5 Bxh2+ 30.Kf1 fxg5 31.d5 Be5
26...Rxf2 27.Kxf2 Bxf4 28.h4 f6 29.Kf3
If 29.gxf6 gxf6 30.Rd7 b5 31.d5 Be5 32.d6 Kf8 33.Bb4 Ra8 34.Rb7
29...Bc1 30.gxf6 gxf6 31.Rd7 Re3+ 32.Kf2 Rh3 33.d5 Bxb2 34.Bxb2 Rh2+ 35.Ke3 Rxb2 36.Rxb7 Kf8 37.Kd4 Ke8 38.d6
If 38.Kc5 f5 39.Kd6 a5 40.Ke6 Re2+ 41.Kf6 f4 with an equal looking position
38...Kd8 39.Kd5 f5

Diagram 1

It was here that Black thought that he had completed the mandatory 40 moves and ended up losing on time, falling short by one move. Black had chances of holding this game to a draw.
0–1

Diagram 2

Black to play and win
New game
1.   .. Ng4 2.Qxd6
If 2.Qxg4 Rf1 checkmate
2.   ..Rf1 checkmate