Kramnik started the match out red hot, winning the first two games to take a quick 2-0 lead. Topalov blundered in the first game to cost himself a draw, and missed chances to both win and draw the second game. Topalov stabilized a bit to draw games three and four, after which Kramnik still held a 3-1 advantage.
Then, the match nearly fell apart. During the rest day before the fifth game, Silvio Danailov (Topalov's manager) made a complaint that Kramnik was using the bathroom far too often during each game, and found this activity suspicious -- implying that Kramnik might be receiving computer assistance. The match's appeals committee believed that the claims about the frequency of Kramnik's bathroom visits were greatly exaggerated, but decided to alleviate the complaints by opening a common bathroom for the two players, rather than allowing each to have a private bathroom. In response, Kramnik's manager (Carsten Hensel) issued a statement making it clear that Kramnik would not continue the match unless the agreed-upon match conditions were upheld, including his right to use the bathroom as often as necessary.
Kramnik Forfeits Game Five
As game five approached, tensions mounted and neither side seemed likely to back down. When Topalov arrived for the fifth game, Kramnik was nowhere to be found. He refused to play under the decision of the appeal's committee, and was forfeited. The match score now stood 3-2 in favor of Kramnik, but the future of the match was in doubt.
With the future of a unified chess title in the balance, an agreement was struck; the original bathroom situation was reinstated, and the appeals committee resigned. Kramnik's forfeit was upheld, but Kramnik agreed to continue the match only while maintaining he had the right to protest the forfeited game at a later date if necessary. This was yet another threat to the successful completion of the match; a Topalov victory could mean endless controversy if the forfeit stood as part of his winning margin.
For a while, it seemed as though this scenario may well play out. While games six and seven were drawn, Topalov broke through to tie the match by winning game eight, and then won the next game to take a 5-4 lead. Kramnik struck back immediately though, winning the tenth game. The final two games were drawn, forcing the match into rapid tiebreaks. Kramnik won the tiebreak 2.5-1.5, avoiding much of the drama that may have followed a Topalov win.
However, that's not to say that there was no controversy after the match. Both during and after the match, Topalov's camp produced statistics that supposedly showed that Fritz 9 (at the time, the most commonly used professional chess engine) would have played a high percentage of the same moves that Kramnik played during the match. These claims were roundly criticized; no information was give as to the methods used to come up with Fritz's favored moves (such as the length of time the software was given to analyze a position), and no statistics were provided for the moves played by Topalov (who had also been accused of computer assistance in the past).
Most public support fell behind Kramnik; Topalov's claims and demands seemed ungrounded, and the behavior of both he and Danailov was widely seen as unsportsmanlike, even though it was ultimately Kramnik's decision to forfeit the fifth game that nearly caused the cancellation of the match. Kramnik remained World Champion until losing his title to Viswanathan Anand in 2007, while Topalov fell out of the World Championship picture until his match with (now champion) Anand in 2010.