Roger Federer

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Roger Federer, of Switzerland, returns to Thiemo de Bakker, of the Netherlands, at the Sony Open tennis tournament in Key Biscayne, Fla., Sunday, March 23, 2014. (AP Photo/Alan Diaz)

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Ivo Karlovic, of Croatia, returns the ball to Roger Federer, of Switzerland, during a match at the Sony Open tennis tournament, Friday, March 21, 2014, in Key Biscayne, Fla. (AP Photo/Lynne Sladky)

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Roger Federer, of Switzerland, leaps into the air after defeating Ivo Karlovic, of Croatia, 6-4, 7-6 (7-4) at the Sony Open tennis tournament, Friday, March 21, 2014, in Key Biscayne, Fla. (AP Photo/Lynne Sladky)

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Roger Federer, of Switzerland, returns the ball to Ivo Karlovic, of Croatia, at the Sony Open tennis tournament, Friday, March 21, 2014, in Key Biscayne, Fla. Federer defeated Karlovic 6-4, 7-6 (7-4). (AP Photo/Lynne Sladky)

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Roger Federer, from Switzerland, returns the ball during practice atthe Sony Open tennis tournament at Crandon Park in Key Biscayne on Tuesday, March 18, 2014. (AP Photo/El Nuevo Herald, David Santiago) MAGS OUT

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Roger Federer, of Switzerland, hits to Novak Djokovic, of Serbia, in the final match of the BNP Paribas Open tennis tournament, Sunday, March 16, 2014, in Indian Wells, Calif. (AP Photo/Mark J. Terrill)