updated 5:29 p.m. ET Aug. 31, 2008

NEW YORK - Second-seeded Jelena Jankovic won her sort of split decision, beating No. 21 Caroline Wozniacki 3-6, 6-2, 6-1 Sunday to reach the quarterfinals of the U.S. Open.

Jankovic went into her trademark splits early in the third set reaching for a shot. She lost the point and stayed splayed on the court, and fans wondered whether she’d hurt herself.

But Jankovic bounced up and easily bounded around the court, quickly finishing off her 18-year-old Danish opponent. Jankovic repeated her victory over Wozniacki from Wimbledon, where the Serbian star also rallied after losing the first set.

“My mom told me that I am losing a little bit of weight,” Jankovic said. “I’m actually not losing weight, I’m just getting firmer, you know?”

Jankovic has never reached the final at a major event. She’s got an outstanding chance to go far this time — the Williams sisters are in the opposite bracket, No. 1 Ana Ivanovic and No. 3 Svetlana Kuznetsova have lost and 2007 Open champion Justine Henin has retired.

Jankovic will next meet No. 29 Sybille Bammer, who got past No. 12 Marion Bartoli 7-6 (3), 0-6, 6-4 in a match that lasted 3 hours, 5 minutes — believed to be the longest women’s match, by time, in U.S. Open history.

Along with a trophy, Jankovic is in the chase to wind up as the world No. 1.

“It’s a goal, but I want to win a Grand Slam,” she said.

Another woman in the chase for No. 1 — and also without a major championship title — is Olympic gold medalist Elena Dementieva, who beat Li Na 6-4, 6-1 and now faces No. 15 Patty Schnyder.

Wozniacki started strong, hitting the ball harder and playing much more aggressively than Jankovic. The scoreboards at Arthur Ashe Stadium malfunctioned early in the second set — even without them, it was clear Jankovic was in trouble.

By the time the scoreboards came back on, Jankovic was on her way to winning the first game of the final set.

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“I just got a bit more defensive. I felt a little bit tired. She took advantage of that,” Wozniacki said. “She was just better than me today.”

Jankovic won without a lot of her typical drama. There was a slight rift in the first set when she seemed to have more trouble with the officials than the wind. Jankovic disputed two line calls on the same point, then decided against calling for a replay challenge.

“Lose it. Who cares?” she told the chair umpire.

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