SHANGHAI - World number one Roger Federer suffered a shock defeat to Fernando Gonzalez to put his Masters Cup defence in doubt on Monday.

The Swiss triple champion raced to a one-set lead but then lost a second-set tie-breaker by a mile before being edged out by the gutsy Chilean 3-6, 7-6 (7/1), 7-5 in front of a disbelieving crowd at Qi Zhong Stadium.

Roger Federer of Switzerland waves to the crowd as he leaves the court after losing his match to Fernando Gonzalez of Chile at the 2007 Tennis Masters Cup Shanghai. Gonzalez upset Federer 3-6, 7-6 (7/1), 7-5. [Agencies] It was a disastrous start from the 12-time Grand Slam winner, who had never lost a round-robin match at the season finale and enjoyed a 10-0 record against the seventh-ranked Chilean.

Federer, whose last match was a quarter-final loss to David Nalbandian at the Paris Masters, also suffered his first back-to-back defeats since 2003.

"It's tough because I thought I played pretty good," said the rueful Swiss.

"In some ways I have regrets and in some ways I don't, because I thought it was ridiculous the kind of shots he was coming up with.

"You have to give him credit for that. I hadn't been broken all the way through until the very end. He lost his serve but then he broke and held his serve, so that's that."

Federer started in typically ruthless fashion, breaking Gonzalez in his first game before wrapping up the first set in just 29 minutes.

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