Federer, Nadal compete at Mubadala World Tennis Championship

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Roger Federer of Switzerland serves the ball to Robin Soderling of Sweden during their match on the second day of the Mubadala World Tennis Championship at the International Tennis Complex in Zayed Sports City in Abu Dhabi, December 31, 2010.

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Roger Federer of Switzerland returns a backhand to Robin Soderling of Sweden during their match on the second day of the Mubadala World Tennis Championship at the International Tennis Complex in Zayed Sports City in Abu Dhabi, December 31, 2010.

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Rafael Nadal of Spain returns the ball to Tomas Berdych of the Czech Republic during their match on the second day of the Mubadala World Tennis Championship at the International Tennis Complex in Zayed Sports City in Abu Dhabi, December 31, 2010.

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Rafael Nadal of Spain returns the ball to Tomas Berdych of the Czech Republic during their match on the second day of the Mubadala World Tennis Championship at the International Tennis Complex in Zayed Sports City in Abu Dhabi, December 31, 2010.

(Reuters)