Defending champion Caroline Wozniacki reached the semifinals of the Dubai Tennis Championships on Thursday, while U.S. Open champion Sam Stosur lost to Jelena Jankovic.

Caroline Wozniacki ousted Ana Ivanovic 6-3, 7-5 in a meeting of former No. 1s, after Jankovic stopped Stosur 6-4, 6-2 Thursday.

Wozniacki eased through the first set and overcame more resistance in the second.

"I'm very pleased to get through that in straight sets," Wozniacki said. "Ana really stepped it up in the second set, took the balls very early, and just played really well. She took her chances and had nothing to lose."

Wozniacki is the highest-seeded player left in Dubai at No. 3 after top-ranked Victoria Azarenka pulled out of the tournament Wednesday because of an ankle injury.

Azarenka unseated Wozniacki from the No. 1 ranking last month by winning the Australian Open. Now at No. 4, Wozniacki says she is determined to regain the top spot — and perhaps win the first Grand Slam title of her career.

It's all possible, Wozniacki said, but there's no pressure.

"You know, a lot of things could happen. I could become the president as well. I could become a billionaire by tomorrow if I win the lottery," Wozniacki said. "But you just need to enjoy winning and enjoy playing."

Wozniacki will play Julia Goerges on Friday after the unseeded German defeated Daniela Hantuchova of Slovakia 4-6, 6-3, 6-4.

Earlier, Jankovic was in control throughout the match while Stosur struggled with her game. The Australian seemed to rush her shots for much of the first set, hitting the ball early and returning it long and wide. Stosur broke Jankovic early in the second, but the Serb broke right back and pulled ahead 5-2.

"I'm happy with the win," Jankovic said. "It's never easy. Against her, we always have tough matches."

She also defeated Stosur in last year's quarterfinals in Dubai.

"I think the key was my return," Jankovic said. "You know, she has one of the best, if not the best, serves in the women's game. It's never easy to return her serve.

"But usually she likes to serve and then start dictating the point with her forehand. I didn't really allow her to do that ... I was pretty much in control the whole time," Jankovic said.

Stosur was disappointed she missed a chance to avenge last year's loss.

"I definitely didn't play as well today," Stosur said. "I mean, she played all right. She served quite well. I felt like I was getting pushed back.

"I think today she stayed up on the baseline quite well and I didn't. It was more that I don't think my forehand was as good as what it needed to be."

Jankovic will meet fifth-seeded Agnieszka Radwanska in the semifinals on Friday. The Polish player advanced after defeating ninth-seeded Sabine Lisicki of Germany, 6-2, 6-1.