US Open 2011: Serena Williams to meet Caroline Wozniacki

Williams won her three US Open titles in 1999, 2002 and 2008

Title favourite Serena Williams will play world number one Caroline Wozniacki in the US Open semi-finals after both won in straight sets.

Williams came through an early test against Anastasia Pavlyuchenkova to win 7-5 6-1 on a bright afternoon on Arthur Ashe Stadium after two days of rain.

And Wozniacki then beat German 10th seed Andrea Petkovic 6-1 7-6 (7-5) after being moved to Court 13.

Sam Stosur will play unseeded German Angelique Kerber in the other semi.

Ninth seed Stosur knocked out second seed and last year's runner-up Vera Zvonareva 6-3 6-3, although it was not a major shock being the Australian's eighth successive win over the Russian.

Stosur had come through marathon wins in her previous two matches and benefited from the rain delays of Tuesday and Wednesday as she saw off Zvonareva in just 67 minutes.

"It's always nicer to finish them off in less than three hours," said Stosur, who took a US Open women's record three hours and 16 minutes to beat Nadia Petrova in the third round.

"To come out and play the way I did today after the long waiting around that we have had to do is really, really pleasing."

Kerber, ranked 92nd, continued her surprise run through the field with a 6-4 4-6 6-3 win over Italy's 26th seed Italian Flavia Pennetta.

Williams progressed to the last four still without having dropped a set, although the early stages against Pavlyuchenkova were among her least convincing of the tournament.

Six successive breeaks of serve at the start of the match told of an even contest but from 5-5, the 13-time Grand Slam champion stepped up a gear and reeled off five games in a row to grab a decisive lead.

"She's definitely different," Williams said of Pavlyuchenkova. "She'll hit hard, then she'll hit soft. She's great at mixing things up.

"I just think I was a step slow in the beginning. I was hitting a lot indoors and it's a totally different surface. Once I kind of got out in the match, once I showed up, I was able to play better."

Wozniacki remains on track to match her run to the final of two years ago as she continues her quest for a first Grand Slam title.

The 21-year-old Dane overcame the disruption of being moved from Louis Armstrong Stadium because of a wet patch on the court, seeing off a second-set fightback from Petkovic to set up a clash with Williams.

"I'm looking forward to that match," said Wozniacki. "She's an amazing athlete and a great girl. She's a fighter just like I am on the court. I got to go out there and take my chances."