Serbia's Novak Djokovic returns the ball against Germany's Philipp Kohlschreiber during the 3rd round competition of men's singles at the French Open tennis tournament at Roland Garros in Paris, France, May 30, 2009. Djokovic lost to Kohlschreiber 4-6, 4-6, 4-6.

"What is disappointing was that I couldn't find the rhythm throughout the whole match. This is what I was always managing to do," said the 22-year-old. "I can't really explain why. Physically I felt good, but it's just a bad day at the office. Of course he played very solid," he added.

This is not the first time the German has caused an upset. He knocked Andy Roddick out of the Australian Open last year, but no one really expected him to trouble the Serb, who some had tipped to overthrow current world number one Rafael Nadal this year.

"I think I played really, really one of the best matches I ever play in a big tournament," said Kohlschreiber, who, with the win, equaled his best grand slam showing of two last-16 appearances at the Australian Open.

"Maybe Novak didn't play his best today. But from my point of view ... I did a really good job today."

Federer had beaten his 35th-seeded opponent three times without a loss but lost his way in the opening set. But Mathieu didn't roll over in front of his home public while the 13-time Grand Slam champion dominated the following three sets and took his second match point with an inside-out forehand winner.

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