Russia's Anastasia Myskina upset top-seeded Lindsay Davenport 7-6, 6-4 at the WTA Championships in Los Angeles on Friday, adding intrigue to the race for the world number one ranking.

With the defeat in the round-robin Red Group, Davenport will almost certainly have to beat fellow American Serena Williams on Saturday to secure a spot in the semi-finals of the eight-woman season ending event.

Second seed Amelie Mauresmo and Wimbledon champion Maria Sharapova both qualified for the semi-finals out of the Black Group when the Frenchwoman knocked out U.S. Open champion Svetlana Kuznetsova 6-3, 6-2 and the Russian out-punched Vera Zvonareva 6-4, 7-5.

If Davenport fails to make the last four and Mauresmo reaches the final, Davenport could lose the number one ranking to the Frenchwoman.

Williams has won both her matches while Davenport and Myskina have a win and a loss apiece, although the Russian has taken three sets to the American's two.

Elena Dementieva is the fourth player in the group but she has yet to win a set and cannot qualify for the semi-finals.

COUNTER-PUNCHING

Myskina counter-punched the more physically imposing Davenport, running down shots and burying them into corners.

The French Open champion, who blew a set and two-break lead against Williams on Wednesday, held off Davenport in the second set after the American battled back from a 3-0 deficit.

"If I had lost this match, that would have been it for the year," Myskina said.

"I told myself to keep fighting and to play every ball and not to think about the score."

Mauresmo and Sharapova have 2-0 records in the eight-woman competition and will play each other on Saturday in what is a meaningless match in the group but will be an important one for Mauresmo, as she needs points to edge closer to Davenport in the rankings.

"The story is very simple: I need to reach the final and probably win the Championships to hope to get to number one," Mauresmo said. "I am very proud to reach the semi-finals but I have to keep going." Davenport said rankings had never been her greatest concern.

"No matter what, even if I finish the year at number two, it's been a great year and if I finish number one, great," Davenport said.

"I've been fortunate to get to number one a number of times. Amelie has played great the last couple weeks. If she continues to do well here, she deserves it."