Anatoly Karpov is clearly not the type of man to over-indulge himself at Christmas. On Boxing Day, he returned to the fray at the Groningen tournament in the Netherlands and took the lead for the first time by winning a delicate endgame against Curt Hansen.

In the diagram position, Karpov, playing White, clearly had the advantage thanks to his extra space and more active bishop, but it hardly looks enough to win.

Play continued 1.c5! dxc5 (bxc5 leaves White with a passed a-pawn after Qxa6) 2.Qxa6 h5 3.Qe2 hxg4 4.Qxg4! Qxg4 5.hxg4 Kf7 6.a4! Ke8 7.a5!

Good timing. The apparently more natural plan of 7.Kc2, trying to bring the king to b5, lets Black escape after ...Kd7 and c6. 7....Kd7 (Instead 7...bxa5 8.Bxa5 Kd7 9.Kc2 c6 10.Kd3 also lets White squeeze out a win) 8.axb6 cxb6 9.Bc3 Bd6 10.b4!! (The key move. Black must not be allowed time to play b5.) 10....cxb4 (10...c4 is met by 11.b5 and White easily rounds up the c-pawn.) 11.Bd2 Kc7 12.Kc2 b5 13.Kb3 Kd7 14.Bxb4 Bc7 15.Bc3 Bd6 16.Bb2! b4.

Black had run out of moves: Kc7 or Ke7 lose to 17.Ba3, while 16...Kc8 17.Ba3 Bc7 18.Bf8 wins after 18...Kb7 19.Kb4 Ka6 20.Kc5 or 18...Ba5 19.Bg7 Bc7 20.Kb4.

The game continued 17.Bc1 Bc5 18.Bd2 Bg1 19.Kxb4 Bf2 20.Kc4 Bg1 21.Kd3 Bc5 22.Be3 Be7 23.Kc4 Ba3 24.Bd2 Be7 25.Bc3 Bd6 26.Bb4 Bb8 27.Kb5 Ba7 28.Bc5 Bb8 29.d6! resigns. After 29...Bxd6 30.Bxd6 Kxd6 31.Kb6 Ke7 32.Kc7 Ke6 33.Kc6 Kf6 34.Kd6 White wins without problems.

Running the bishop out of moves at b8 was a neat finishing touch. After seven rounds at Groningen, Karpov leads with 41/2 points. Kamsky, Leko, Sokolov, Svidler and Van Wely are half a point behind. Michael Adams is languishing on 21/2.