Open positions need careful assessment

Sometimes when the position appears evenly balanced, there are chances that a player might relax just that tiny bit and make a careless move.

In the game which follows, the position is evenly balanced but Black plays a innocuous but careless rook move which suddenly changes the balance. A weak rook move  in the ending and Black suddenly finds himself at the losing end.

White: Bjorn Ahlander (2436) – Black: Tom Wedberg (2487)
Scandic Hotels CC Stockholm ,1999
Nimzo-Indian Defence

1.d4 Nf6 2.c4 e6 3.Nc3 Bb4 4.Qc2 0–0 5.e4 d5
This is not a frequently played line. Here Black has many moves at his disposal like 5...c5 Nc6 6.Nf3 d6 7.Be3 Bxc3+ 8.bxc3 e5 9.d5 Nb8 10.c5 Ng4 11.Bg5 f6 12.Bd2. Also played is 5...d6
6.e5  If 6.cxd5 exd5 7.e5 Ne4 8.Bd3 c5
6...Ne4 7.Bd3 c5 8.cxd5 exd5 9.Nge2 cxd4  Black ahs a better option in  9...Nc6
10.Nxd4 Nd7 11.f4 Qh4+
The Queen springs into action with a check. Black can play 11...Ndc5 12.0–0 Bxc3 (12...Nxd3 13.Qxd3 Bc5 14.Be3 Bxd4 15.Qxd4 Nxc3 16.bxc3) 13.bxc3 Qa5
12.g3 Qh3  However tempting the move 12...Nxg3 may be to continue the attack, it loses immediately because of: 13.Qf2 Nc5 14.Bc2 Nce4 15.Bxe4 dxe4 16.Qxg3
 13.Bf1 Retreating back the bishop for defence! If 13.Bxe4 dxe4 14.Qxe4 Nc5
 13...Qh5 14.Bg2 Nb6
If 14...Qg6 15.Bd2 Bxc3 16.Bxc3 Qa6 17.Qe2 Qxe2+ 18.Nxe2 white will have a positional advantage in the endgame
 15.a3 Till now the players were following a previously played line but now White deviates with anew move. If 15.0–0 Bxc3 16.bxc3 Bh3 17.f5
 15...Bxc3+  If  15...Bc5  16.Nxd5 Bxd4 17.Ne7+ Kh8 18.Qxe4 Rd8 19.f5 is better for White
16.bxc3 Bh3 
Here Black can also look at 16...Bf5 
17.0–0 After some tricky moves, White finally castles! If 17.Bxe4 dxe4 18.Qxe4 Rac8
17...Bxg2 18.Qxg2
If 18.Kxg2 Rac8 is slightly better for Black
18...f5 If 18...Nxc3 19.g4 Qh4 20.Nf5 Qd8 21.Bb2 And if  18...Rac8 19.g4 Qh4 20.Nf5 Qd8  19.exf6 ( en-passant) Nxf6
The position more or less is equal after 19...Rxf6
20.f5 White decides to march into enemy territory
20...Rac8  If  20...Ne4 21.g4 Qh4 22.Ne6 Rf7
21.Ne6 Rfe8 If 21...Rf7 22.Be3 
22.Be3 Rxc3 23.Bd4 Rc4
Better appears 23...Rc6 
24.Rad1 Rec8 25.h3
A  mistake! White plans to push his King side pawns which does not look like a good idea
25...Rc2 Infiltrating into the seventh rank
26.Rd2 Rxd2 27.Qxd2 h6
If  27...Qxh3  28.Qg5 g6 (28...Nh5 29.f6 And if 28...Ne8 29.Nxg7 h6 30.Qg6 And if 28...Qg4 29.Bxf6) 29.Nf4
28.Qg2 Qf7 29.g4

Diagram 1

29. ..Re8  A mistake! Black could have maintained balance with 29. ..Nc4 or 29. .Nbd7. If 29...Nbd7 30.h4 Nf8 31.g5 hxg5 32.hxg5 Nh5 33.g6 Qd7 34.Qg5 And if 29...Qe7 30.h4 Rc4 31.g5 31...hxg5 32.Qxg5
30.h4 Rxe6 31.fxe6 Qxe6 32.g5 hxg5
Black can think about  32...Ne4
33.Qxg5 Nbd7
If 33...Ne8 34.h5 Qe4 35.Bc3
34.h5 Qg4+ If 34...Qf7 35.h6 Kh7 36.hxg7 Qxg7 37.Qxg7+ Kxg7 38.Bxa7
35.Qxg4 Nxg4 36.Rc1 Ndf6
If 36...a6 37.Rc7 Ndf6 38.Rxb7 Nxh5 39.Rd7Ngf6 40.Ra7
37.Bxf6 Nxf6 38.Rc7 b5
If 38...a5 39.Rxb7 Nxh5 40.Ra7 Nf4 41.Kf2  39.Rxa7 Ne4 40.Kf1 Kh7 41.Ke2 Nd6 42.Kd3 Nc4 43.Ra6 1–0

Diagram 2

White to play and win
1.Rxh7+ Kg8 2.Rh8 check-mate.