ISTANBUL (AP) -- Li Na outlasted former doubles partner Jelena Jankovic 6-3, 2-6, 6-3 Thursday for her second victory at the WTA Championships.
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.
Eight-seeded Angelique Kerber upset No. 3 Agnieszka Radwanska 6-2, 6-2 to remain in contention for the semifinals. Radwanska (0-3) was eliminated in the round-robin tournament that features the top eight players in the world. The top two finishers in each pool advance to the semifinals.
Kerber (1-1) 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 semifinals for the first time. Seventh-seeded Jankovic is 1-1. Jankovic is back in the tournament for the first time in three years. Victoria Azarenka also is vying to make the semis from the group.
''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 U.S. 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.