Updated

By Larry Fine

NEW YORK (Reuters) - Kim Clijsters was relieved to emerge with a victory but concerned she might not be so fortunate in her semi-final showdown against Venus Williams unless she improved her serving.

"I didn't play a good match, but I was obviously able to win it," the defending champion told reporters after a mistake-marred 6-4 5-7 6-3 win over fifth-seeded Australian Samantha Stosur on Tuesday.

Blustery winds bothered both players from the service line. Stosur was broken eight times and the Belgian lost seven service games. At one stretch, nine of 10 games went against serve, including the first six games of the last set.

Clijsters, who committed eight double faults, steadied herself at the end and held her last two service games to claim victory, ending the nearly two-hour match with an ace.

"The next match everything will have to be a lot better," said Clijsters, who registered 43 unforced errors. "My serve hasn't been going the way that I want it to go.

"I think it's because when I play players who play aggressively, I tend to not finish off my service motion properly.

"In my movement, as soon as I land on my left foot, which normally you're supposed to land forward, I'm already pushing off to try to get to the next shot. I know that that's not what you're supposed to do. But, yeah, I mean, 20 years of tennis."

Although Williams is playing for the first time since Wimbledon because of a knee injury, the 27-year-old Clijsters said the American two-time U.S. Open champion was playing "some of her best tennis for a while."

The two have split 12 career meetings with Clijsters winning the last four, including two wins at the U.S. Open., yet the Belgian was hardly comforted by the ledger.

"The way that she's been playing and the way that she has mentally looked, I think it's maybe been even been good for her to have been away for that long, because she looks more hungry than ever."

(Reporting by Larry Fine, Editing by John O'Brien)