Jack Sock serves the ball against Michael Berrer, of Germany, during a match at the Citi Open tennis tournament, Tuesday, July 29, 2014, in Washington. (AP Photo/Nick Wass)

Washington Tennis

Jack Sock serves the ball against Michael Berrer, of Germany, during a match at the Citi Open tennis tournament, Tuesday, July 29, 2014, in Washington. (AP Photo/Nick Wass)

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