- WTA Championships
Serena through, but Radwanska headed home
Top-ranked Serena Williams became the first player into the semi-finals of the WTA Championships by sweeping aside Petra Kvitova 6-2 6-3.
The defending champion, who won all three matches in her group without dropping a set, is bidding for her fourth title in the eight-women, season-ending tournament.
Li Na also remains unbeaten after she outlasted former doubles partner Jelena Jankovic 6-3 2-6 6-3.
The key to the error-filled match full of long rallies was Li's break of serve in the third set for a 4-3 lead. Jankovic hit a backhand into the net on Li's second match point.
Eighth-seed Angelique Kerber upset No. 3 Agnieszka Radwanska 6-2 6-2 to remain in contention for the semi-finals.
The result means Radwanska, who has lost all three of her matches, is eliminated from the tournament that features the top eight players in the world in two groups, with the top two in each pool advance to the last four.
Kerber earned her first win at the elite event after going 0-3 last year.
The fourth-seeded Li has a 2-0 record in the White Group and looks likely to advance to the semi-finals for the first time. Seventh-seeded Jankovic is 1-1. Jankovic is back in the tournament for the first time in three years.
"It was tight, yeah, but at least it's better than the last two years," Li said. "Playing Jelena is always tough, today I was running a lot, forward and backward."
Li beat Jankovic 6-3 6-0 in the round of 16 at the US Open and holds a 6-4 career edge over her Serbian friend.
"She was a No. 1, so she has the level to be in the top 10. She has more confidence now," Li said.
Both players struggled with consistency. Li had 45 unforced errors and 21 winners, and Jankovic produced 36 unforced errors and 17 winners.
"I managed to come back in the second set and played really well there, served much better," Jankovic said. "In the third set, it was just a couple of points. I got broken in that (seventh) game. She lobbed me and the ball went on the line."
Li followed the lob with a crisp backhand winner to take the game.
"They were the crucial points at that stage and made a difference," Jankovic said.
Download ESPN's new UK sport app, a fresh and powerful new way to follow your favourite UK sports news, scores and video.