Kim Clijsters [Images] recovered to beat Venus Williams [Images] in a dramatic US Open [Images] quarter-final on Tuesday night, and then admitted she had not been sure whether she would ever return to the level she was at before the wrist surgery that caused her to miss most of 2004.

The fourth seed thrilled the late-night crowd at Flushing Meadows as she fought back from a set and 4-2 down to stun Wimbledon [Images] champion Williams 4-6, 7-5, 6-1 and secure a semi-final spot against Russian top seed Maria Sharapova [Images].

• Clijsters recovers to beat Venus | Images from day 9

Having won six titles in 2005 since returning to the tour in March, Clijsters arrived in New York as the tournament favourite, but the Belgian said her win over Williams is the biggest since her surgery.

"Since my injury, every win just means a lot more," said the former world number one.

"This victory means a lot, especially after not knowing if I was going to be able to play this type of level again, that definitely means so much more than it used to."

Clijsters said her defensive scrambling, which saw her do the splits at one stage, had been important in her victory.

"Even though I probably wasn't playing my best tennis at all, for a set and a half, I was still fighting," she said.

"I was defending well. I think that's kept me in a lot of the games... We had a lot of long rallies, and I think that got her tired.

"I noticed that she wasn't running as well as she used to. And not moving as well. I knew that if I would win that second set I was going to have a good chance to win because I felt fine."

Williams was at a loss to explain her defeat.

"I think I was playing decent," Williams said.

"And she started playing really bad, and it totally threw me off. She started hitting these really weird shots and short balls and just weird stuff.

"Next thing I knew, I was playing as bad as she was, and she was able to recover, it seemed like I just wasn't."

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