Li Na battles past Jankovic

Li Na defeated Jelena Jankovic at the WTA Championships on Thursday, meaning the battle for the two semifinal spots in the White Group will go on.

Li had routed Jankovic in the fourth round of the US Open, but this time it was a much different story as the two battled two hours and 11 minutes before the No 4-seeded Chinese emerged with a 6-3, 2-6, 6-3 win over the No 7 seed Serbian.

It was an extremely streaky match -- never did either player win fewer than two games in a row at any point -- but Li held her nerve well towards the end, winning three straight games from 3-all in the third set to emerge victorious in the lone game of the season-ender on Thursday.

Li is now 2-0 in the White Group, while Jankovic and Victoria Azarenka are 1-1, and Sara Errani 0-2.

World No 1 Serena Williams beat Agnieszka Radwanska for the eighth time in eight matches to move ominously towards the semifinals on Wednesday.

The American was again too strong for the Pole in a 6-2, 6-4 victory to stay in charge of Red Group with one more round-robin match to come against Petra Kvitova, another player to whom she has never suffered defeat.

“Radwanska definitely played pretty well. Am I happy? I guess. I'm happy to still be alive in the tournament. But, you know, I can always look to improve on some things,” Williams told reporters after her 75th match win of a dominant year.

Radwanska, whose only set against the 32-year-old Williams came in the 2012 Wimbledon final, is unlikely to survive the group after two defeats so far.

Del Potro shines

Top seed Juan Martin del Potro defeated Marcos Baghdatis for the second time in a month on Thursday to advance to the Swiss Indoors quarterfinals on Thursday at Basel.

Defending champion Del Potro followed up on his Japan Open victory over Baghdatis, the 2005 finalist, with a 6-1, 6-2 win in 73 minutes. The Argentine bext faces qualifier Paul-Henri Mathieu, who defeated Michael Llodra 6-4, 6-3.

Vasek Pospisil reached his third ATP quarterfinal as he defeated Tomas Berdych’s conqueror, Ivo Karlovic, 6-3, 6-3. France’s Edouard Roger-Vasselin built on his first-round upset win over Stanislas Wawrinka by reaching the quarterfinals with a 7-5, 6-3 win over Tobias Kamke.

Roger-Vasselin meets Daniel Brands in the last eight after the German defeated Lukasz Kubot 6-2, 6-4.