Clijsters, Sharapova Mentally Shaky at WTA Championships

The Belgian looked in control after fighting off a match point in the second set and going up a break 3-1 with triple break point on her opponent's serve in the third, but it was Pierce who played the more controlled baseline game in the end after admittedly getting tight.

"The third set was a battle," Pierce said. "I kept fighting and hanging in there."

Clijsters, who won the year-end championship in 2002-03 before sitting out last year with a wrist injury, is now likely a big proponent of the round-robin format.

The Belgian can ill afford to lose another match against her group mates, while wins against remaining opponents Amelie Mauresmo and Elena Dementieva can still advance her into the Saturday semifinals with a 2-1 round robin record. A combination of another loss in the round robin for Clijsters and Lindsay Davenport advancing to the semifinals would clinch the year-end No. 1 ranking for the American.

Clijsters, like Davenport, said she had a hard time seeing the ball in the Staples Center set-up, and admitted she will need to get her head together to rally for a semifinal berth.

"I was not seeing the ball at all," Clijsters said. "With the lights, it felt too bright and it was hurting my eyes. My mind was not ready to play a match. These kind of days happen."

Defending champion Maria Sharapova narrowly avoided the upset bug Tuesday in her round robin debut, rebounding from a second-set loss to defeat Swiss left-hander Patty Schnyder 6-1, 3-6, 6-3.

The Russian, who also played sparingly toward the end of the year due to injuries, was another player looking mentally unprepared to go into big-match mode.

"It was up and down," Sharapova said. "I felt a little awkward in some situations because I haven't been match tough lately. I'm absolutely exhausted."

Schnyder had won her previous meeting with Sharapova this year on clay.

"It took me a while to get into the match," Schnyder said. "She started off hitting so fast and serving well. It is very hard to play the first shot good enough that she is not really dominating the point from the start. And it was just so tough to reach for her serve. She put a lot of slice on that first serve. But I think I played a great second set. And at the end, I even had a chance to break back and even make the big point which was -- I should have made it."

The night ended with world No. 1 Lindsay Davenport improving her career record to 7-0 over Russian Nadia Petrova.

"I've always struggled a little bit here because there's no backdrop," Davenport said of the Staples Center. "I lose my depth perception...I really wanted to start off with a win here. I was able to do that last year, and I still didn't make it out of the round robin. So I know I can't take this for granted."

Davenport is on a three-tournament streak, winning all three events she contested following this year's US Open before being sidelined with the flu and skipping the last regular-season stop in Philadelphia.

Tuesday's line-up features a presumably well-napped Clijsters in a must-win vs. Mauresmo (Belgian leads head-to-head 8-2), Davenport vs. Schnyder in a must-win for the Swiss (American leads 8-2), and Pierce facing Dementieva (Russian leads 3-1).