ISTANBUL -- Maria Sharapova pulled out of the WTA Championships with a sore ankle Wednesday after losing her second straight match at the season-ending tournament.
Sharapova entered the tournament after sitting out since withdrawing in the quarterfinals in Tokyo last month because of an ankle injury.
After losing 7-6 (4), 6-4 to Li Na in her second round-robin match Wednesday, Sharapova said "the ankle didn't recover as well as I had hoped after the first round."
Sharapova lost to Samantha Stosur in her opening match on Tuesday.
"The swelling got a little worse," the second-ranked Russian said. "It just limits my movement a lot, and it's not something I really want to risk, especially at the end of the season, knowing that I have some time to recover and let it heal naturally instead of really pushing it and damaging something else."
The Russian will be replaced by alternate Marion Bartoli of France, who will face Victoria Azarenka of Belarus in the final group round. Azarenka maintained her perfect record against Sam Stosur with a 6-2, 6-2 win earlier Wednesday.
Wozniacki fell to 1-1 in the round-robin phase after losing 6-2, 4-6, 6-3 against Zvonareva in the late match. Even with the loss, she will finish at No. 1 in the rankings for the second year in a row, despite never having won a major. Sharapova was the only player with a chance to overtake the Dane going into the tournament.
"It's amazing for me to finish the year as No. 1 once more," Wozniacki said. "I mean, only very few players have finished a year as No. 1, and to do it two years in a row is very special. I'm only in the beginning of my career, and to have achieved so much already, it's a dream come true."
Sharapova led 4-2 in the first set before Li broke back to force the tiebreaker, where the Russian let a 4-0 lead slip away. Li then took a 5-2 lead in the second and served out the match on her second attempt.
Sharapova said she expects to return to the court in Brisbane next year ahead of the Australian Open.
"Obviously disappointing to end it this way," the Russian said about her season. "But I have no regrets. ... I definitely progressed from last year and I've improved, and my game has stepped up. I still feel like going into next year there's so many things that I can improve that can make me better. It's just something I look forward to when I start training again."
Li, the French Open champion, is the first Chinese player to qualify for the season-ending event for the world's top eight players.
Stosur, the U.S. Open champion, was coming off her first ever win over Sharapova on Tuesday but appeared flat as she came out for Wednesday's opening match. In her first match in the White Group, the fourth-seeded Azarenka broke four times to take her head-to-head record against Stosur to 5-0.
"I didn't play aggressive enough ... I don't feel like I did anything," Stosur said. "I just kind of got pushed around the court, and eventually was made to make an error or she would hit a winner."
The Australian said her performance wasn't affected by the late match against Sharapova the previous evening.
"Oh, I can't blame that," she said. "Yeah, it was a quick turnaround, but I felt like I was ready to go."