After six rounds of the Madrid tournament, Viswanathan Anand is a point ahead of the field. Scores: Anand 41/2; Leko and Svidler 31/2; Krasenkov, San Segundo, Illescas and Adams 3; Yermolinsky 21/2; Granda Zuniga and Belyavsky 2.

Anand increased his lead with a win against Illescas in round six when he took the White side of an opening variation that he has previously shown himself happy to play as Black. The position after 12...Bg4 is one of the trickiest problems for modern theory. Black's queen is out of play and White has an imposing pawn centre, but does this compensate for Black's extra pawn? Anand certainly made it look as though it did.

In the earliest days of this variation White generally played 13.Be3. Then came the idea of 13.Bg5, meeting 13...h6 with 14.Be3 (14.Bxe7 Re8 poses Black no trouble) in the hope of gaining time later with Qd2 or Qc1, but here Anand's 14.Bh4 introduced a new idea. In no hurry to try to regain his extra pawn, he set out to prove that his one-pawn central majority was better than Black's two pawn advantage on the Q-side. After 19.e5, 20.e6 and 21.Rxe6, the threat of 22.d6 followed by Bd5 left Black struggling.

White: Viswanathan Anand

Black: Miguel Illescas

1 d4 Nf6 18 Bxf3 Nd7

2 Nf3 g6 19 e5 Rac8

3 c4 Bg7 20 e6 fxe6

4 Nc3 d5 21 Rxe6 Nf6

5 cxd5 Nxd5 22 Rxe7 Qc2

6 e4 Nxc3 23 d6 Qxd1+

7 bxc3 c5 24 Rxd1 a5

8 Rb1 0-0 25 h3 a4

9 Be2 cxd4 26 Rc7 Kh8

10 cxd4 Qa5+ 27 Rdc1 Rb8

11 Bd2 Qxa2 28 Ra7 Nd7

12 0-0 Bg4 29 Rcc7 a3

13 Bg5 h6 30 Bd5 b5

14 Bh4 Rd8 31 Rxd7 Rxd7

15 d5 g5 32 Rxd7 b4

16 Bg3 b6 33 Bb3 Ra8

17 Re1 Bxf3 34 Rb7 resigns