Denmark's Caroline Wozniacki will end the year as world number one for the second season running despite losing to Vera Zvonareva at the WTA Championship.
Wozniacki lost 2-6 6-4 3-6 but secured the crown when nearest rival Maria Sharapova pulled out with an ankle injury after losing 6-7 4-6 to Li Na.
"It just limits my movement a lot, and it's not something I really want to risk," said Sharapova.
Sam Stosur, who beat Sharapova in her first match, lost to Victoria Azarenka.
Sharapova, who will be replaced in the elite eight-player field by France's Marion Bartoli, added: "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."
In the final match of the day,Zvonareva, who had lost the previous two meetings againstWozniacki, broke the Dane's serve twice in the opening four games to lead 4-0 before clinching the first set in just 34 minutes.
In the second set, the games went with serve until the 10th when the 21-year-old Wozniacki broke the Russian's serve for the first time to take the set.
Zvonareva, who beat Wozniacki earlier this year in the final of the Qatar Open, then took a 4-1 lead in the third before closing out the match.
With one win and one loss in the Red Group, Wozniacki could still miss out on the semi-finals of the season-ending event even if she beats Wimbledon champion Petra Kvitova on Thursday.
Earlier, Sharapova raced to a 4-1 lead over Li before her Chinese opponent levelled at 4-4.
The match went with serve for the remaining four games and despite Sharapova making 72% of her first serves in the opening set, she collapsed from 4-0 up in the tie break to lose 7-4.
Li powered to a 5-2 advantage in the second and the world number five managed to hold her nerve on match point to take the win.
Belarusian world number fourAzarenka strolled to a 6-2 6-2 win over US Open champion Stosur in just one hour and 18 minutes.
However, Stosur, the world number seven, can still qualify for the semi-finals if she beats Li in her last round-robin match.