Maria Sharapova swept past Sam Stosur 6-0, 6-3 at the WTA Championships on Friday to retain a small chance of finishing the year as the No. 1-ranked player.
But if Victoria Azarenka beats Li Na in the final match of the day, Azarenka will be assured of staying No. 1.
Agnieszka Radwanska became the third player to advance to the semifinals when she edged Sara Errani of Italy 6-7 (6), 7-5, 6-4 in a match that lasted 3 1/2 hours. The fourth-ranked Radwanska will play Serena Williams on Saturday.
Sharapova had already qualified for the semifinals of the elite, eight-woman event and has won all three of her round-robin matches.
The Russian rolled through the first set, allowing Stosur only five points. Stosur was an alternate who replaced defending champion Petra Kvitova, who withdrew because of illness.
"I certainly didn't want to play as long a match as I did in the previous round. I wanted to do a better job of a few things and I think I did," said second-ranked Sharapova.
Stosur put up more of a fight in the second set, but Sharapova ended it with a smash. Sharapova won the French Open this year and briefly held the No. 1 ranking.
Errani finished the tournament with a 1-2 record. The seventh-seeded Italian won a game in the middle set that went nearly 15 minutes. But she later dropped serve to fall behind 6-5.
Radwanska served out the set and opened up a 3-0 lead in the final set to secure a place in the semifinals.
Williams was undefeated in three matches in her Red Group and didn't play on Friday.