U.S. Open champion Svetlana Kuznetsova [Images] was at a loss to explain her sudden meltdown against Maria Sharapova [Images] in the quarter-finals of the Australian Open [Images] on Tuesday.

Kuznetsova looked in control of the match when she won the first set and broke her fellow Russian's serve in the opening game of the second.

But then her normally reliable game disintegrated and she crashed to a 4-6, 6-2, 6-2 defeat in 137 minutes.

"It was just terrible. I was very focused and I played very well in the first set but something happened," Kuznetsova told reporters.

"I just stopped playing. My body was there but my mind wasn't there at all.

"I didn't deserve to win because I just didn't fight."

Kuznetsova appeared to lose confidence in the face of 17-year-old Sharapova's fightback, with her serve the biggest casualty.

She failed to hold serve in the last two sets, surrendering eight straight service games. In her final service game she lamely handed Sharapova her first match point with a double fault.

"I was so upset with what happened in the third set. I know what I did wrong but I couldn't concentrate on the moment," said Kuznetsova, 19.

SWITCHED OFF

"I had the match in my hands, I had everything. I just switched off."

Kuznetsova was at the centre of a scandal when a Belgian politician wrongly accused her of a doping offence on the eve of the championship. She was cleared of any wrongdoing and said she planned to sue him but did not allow it to distract her from her tennis.

Kuznetsova, seeded fifth, also refused to blame the heat after her game wilted on a scorching hot Rod Laver Arena where the temperature reached 33 degrees Celsius (91 degrees Fahrenheit).

Fourth seed Sharapova, the Wimbledon [Images] champion, was also struggling physically but Kuznetsova said the difference was her mental state.

"It's all in the mind, you know. I have the game, I have everything, if I don't do the right things, I don't win," said Kuznetsova.

"She played unbelievable. The most thing she's improved I think is in her mind. She's mentally tough. She's very confident in herself.

"She's improved her shots, definitely, but I think the most (important) thing is her mind.

"If I want to be number one, if I want to go more forward, if I want to win more grand slams, I just have to change totally."

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