The 23-year-old Serbian advanced to the quarter-finals of the year's last major tennis tournament, rallying in blustery conditions at Arthur Ashe Stadium on Sunday to defeat an 18-year-old who won August WTA titles at Stockholm and New Haven.

"In the first set she played quite solid. I was the one who was all over the place. I couldn't find my rhythm in these conditions and she took advantage of that," Jankovic said.

"I stayed calm and composed and knew I had to do something to change that. In the second set I did the smart things and I cruised through the second and third set."

Jankovic, who spent a week as world number one earlier in August, will next face Austrian Sybille Bammer, who defeated French 12th seed Marion Bartoli 7-6 (7/3), 0-6, 6-4.

"It's a miracle I could manage three sets," said Bartoli, who was weakened by a sick stomach and defied doctor's advice not to play because of low blood pressure.

Jankovic is 6-1 lifetime against Bammer, most recently beating her in last year's US Open fourth round. Defeating her again to reach the semi-finals would give Jankovic a chance to reclaim the top spot depending on how rivals fare.

With top seed Ana Ivanovic of Serbia and Russian third seed Svetlana Kuznetsova already ousted, this is a prime chance for a Slam breakthrough.

"I want to win a Grand Slam," Jankovic said. "By winning a Grand Slam I would regain the number one ranking again. It's something I want to achieve again."

Jankovic is among five players who could be number one after the Flushing Meadows fortnight, with Serena Williams, Russians Elena Dementieva and Dinara Safina and Ivanovic also still in the mix.

"It would be nice to come back to the number one spot," Jankovic said. "It would be great if I can do it. We will see what happens."

Jankovic reached the French and Australian Open semi-finals but was upset in the fourth round at Wimbledon by Thailand's Tamarine Tanasugarn after hurting her knee in a third-round victory over Wozniacki.

"I have been injured. Right now I finally do not have any problems," Jankovic said. "Little by little I feel like I'm getting better every day.

"I feel the shots a lot better than I did at the beginning of the tournament. That's my goal, get my game together by the end of the tournament."

Jankovic was down a set and in a fight during the second before cracking the Danish teen on her third break-point chance of the sixth game for a 4-2 edge.

"I started well. I played aggressive," Wozniacki said. "The second set, I got a bit more defensive. Even though I was hitting the ball, it wasn't going well. She kept coming in and forcing play. She was just better than me."

Jankovic, who also lost the first set to Wozniacki this year at Wimbledon, broke again to finish the second set and again in the fourth and sixth games of the third set to secure the triumph.

"I'm getting better each day. I'm improving on my fitness," Jankovic said. "I can push off better. Little by little I'm putting the pieces together. I'm bringing my game to the next level. I believe in myself."

Olympic champion Dementieva, who can take the top spot if she reaches her first Grand Slam final since the 2004 US Open, defeated China's Li Na 6-4, 6-1 in just 61 minutes.

The Russian fifth seed booked a quarter-final date against Swiss 15th seed Patty Schnyder, who rallied to defeat Slovenia's Katarina Srebotnik 4-6, 6-3, 6-3.

Dementieva, who is 9-8 lifetime against Schnyder, was delighted by her Beijing triumph but also a bid saddened.

"That was a very special moment for me and my family," she said. "I'm just a little sad that the greatest moment of my life passed me by. I will try for another championship here."