New York: Serena Williams shrugged off a shaky start to book a semifinal berth at the US Open on Thursday, while Samantha Stosur ended Vera Zvonareva`s bid to reach the final for a second straight year.
Williams, whose 13 Grand Slam titles include three US Open triumphs, struggled early with her serve but looked her usual overpowering self by the time when wrapped up a 7-5, 6-1 victory over 20-year-old Russian Anastasia Pavlyuchenkova.
The American has reached the final four without dropping a set will face world number one Caroline Wozniacki in the final four.
Their match was moved from the water-logged Louis Armstrong Stadium, where the legacy of days of heavy rain was water seeping up through the court surface behind one baseline.
Williams and Pavlyuchenkova had briefly taken the court on Wednesday night, but they never got beyond their warm-up before drizzly rain prompted officials to cancel the night session as weather prevented completion of any matches for the second straight day.
Williams said her days of indoor practice may have contributed to her erratic start.
"Maybe that had something to do with it," said Williams, who said she told herself not to get upset with her early errors. "Indoors I think is a little faster."
Stosur, on the other hand, may have benefitted from two days of enforced rest.
After a pair of marathon victories in the third and fourth rounds, she needed just 67 minutes to defeat world number two Zvonareva 6-3, 6-3.
Her third-round victory over Nadia Petrova took a US Open women`s record three hours and 16 minutes, and she rebounded to beat Maria Kirilenko on Sunday after dropping a 17/15 second-set tiebreaker to the Russian.
The ninth-seeded Australian extended her dominance over Zvonareva, beating her for the eighth straight time.
Stosur never faced a break point and fired 25 winners against Zvonareva, who said the Aussie was just too good for her on the day.
"She was able to hold her serve pretty easy, that`s why she could take a lot of risks on mine," said Zvonareva, who has yet to return to a Grand Slam final after runner-up finishes at Wimbledon and Flushing Meadows last year.
"She was over-playing me a little in every game."
Stosur faces either 26th-seeded Italian Flavia Pennetta or unseeded German Angelique Kerber for a place in the final.