Bulgarian chess star Veselin Topalov and U.S. champion Gata Kamsky finished Tuesday with a tie at the 43th move in the sixth game of the World Chess Challenge in Sofia.
Topalov, who played black, is leading Kamsky after three draws, two wins and one loss. The seventh game will take place on Thursday at Sofia's National Palace of Culture and Topalov will have the white pieces.
The World Chess Challenge Sofia 2009 will continue until 28 February. The winner will compete for the world title against reigning world champion Viswanathan Anand of India.
There are at least two more matches to go, and if their points are even, Kamsky and Topalov will then meet in a tiebreak.
Topalov, a former world champion, is currently ranked No. 1 in the world. He has been among the world's best players for years, but it was only after the retirement of Garry Kasparov in 2005 that he broke through to the top.
Kamsky, No. 17 in the world, was a prodigy. He rose as high as No. 4 by the time he was 21, played a match for the title in 1996 and then abruptly quit for eight years.