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)

Sony Open Tennis

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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