Second seed Serena Williams [Images] admitted closing the roof on Rod Laver Arena because of the soaring temperatures helped her battle back from a first set deficit to beat Svetlana Kuznetsova [Images] 5-7, 7-5, 6-1 on Wednesday.

The American's victory prevented a Russian sweep of the Australian Open [Images] semi-finals and she will now play Elena Dementieva [Images] in the last four on Thursday. Vera Zvonareva [Images] and Dinara Safina meet in the other match.

"It was definitely hot," Williams told reporters. "I think it did because it was really hot out there," she added of whether the roof being closed had helped her.

"I was just trying to prepare myself for it to be open the whole time. But with the roof closed it was definitely helpful."

With the air temperature exceeding 43 degrees Celsius, neither Williams nor Kuznetsova looked comfortable in the first set, constantly seeking shade at the end of the court between points.

Williams was broken three times while Kuznetsova was broken twice and the Russian managed to seal the first set shortly after the extreme heat policy was invoked at Melbourne Park.

Both were then forced off the court for 30 minutes until the roof was closed.

Seemingly rejuvenated out of the energy sapping heat, Williams managed to break Kuznetsova when the Russian served for the match in the second set before taking the contest into a decider, which she raced through in just 27 minutes.

DISAPPOINTING FORM

Despite advancing to her 15th Grand Slam semi-final, Williams added she felt she is not playing well.

"It's really encouraging because this whole tournament I felt I've been off and I haven't been playing my best," she said.

"I was happy because I really wasn't playing my best. My balls started flying.

"I was thinking, 'wow, this is just not my best tennis, or even close to it'.

Williams, who is seeking her 10th Grand Slam title, entered the tournament looking fitter than she has in many years at the first Grand Slam of the season said maybe all the work she did in the off-season is affecting her ball striking.

"I don't know, maybe I overtrained. I worked really hard," she said when asked why she thought she was playing poorly.

"I was really ready. Nothing I did in practice... I've been able to do on the court so far.

"It's been really kind of frustrating. I'm thinking I could have been at a pool instead of training."

While she admitted closing the roof had helped her recover, a fear of flying home early had also assisted when Kuznetsova was serving for the match in the second set.

"I was thinking, 'okay, if you lose, you're going to fly coach [economy class] all the way back to Florida [Images]. How uncomfortable would [that] be?'

"I wouldn't allow myself to have the emergency row either. I would be so mad, I would have to sit [in] like the last row, the tightest row.

"That motivated me to do a little better."

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