US Open champion Samantha Stosur secured her place in the semi-finals of the WTA Championships in Istanbul with a commanding 6-1 6-0 win over Li Na.
The White Group match was a decider to see who would join Victoria Azarenka in the last four but French Open winner Li succumbed in 66 minutes.
Vera Zvonareva also made the semis at the expense of Agnieszka Radwanska who lost 7-6 (7-4) 6-3 to Petra Kvitova.
Wimbledon champion Kvitova had already qualified and will play Stosur.
Zvonareva, who squeezed through via a better games percentage than Radwanska and world number one Caroline Wozniacki after they all recorded one win, will play Belarusian Azarenka on Saturday.
Poland's Radwanska, the world number eight who was the last player to qualify for the event, needed only to win a set to claim the runners-up spot in the Red group ahead of Russian Zvonareva, the rival she beat on Thursday from three match points down.
Radwanska was 5-2 ahead in the first set and at deuce in the eighth game, but eventually succumbed to the Czech number three seed Kvitova.
"I just found the rhythm when I really needed it," said Kvitova.
Australian Stosur proved far too strong for China's Li, with a highly effective top-spin serve and some powerfully struck groundstrokes.
"It was a very solid match for me, she said. "I felt really good out there again and hit lots of winners and moved well."
Azarenka, already sure of finishing top of her group, lost her third and last round-robin match 5-7 6-4 6-4 to France's Marion Bartoli, a substitute for the injured Maria Sharapova who withdrew after two matches.
Bartoli has now finished the 2011 season with 58 wins, second only to world number one Caroline Wozniacki, and played more matches than any other player - 82, two more than Wozniacki.