Philipp Kohlschreiber

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Rafael Nadal, of Spain, serves the ball to Philipp Kohlschreiber, of Germany, during the Miami Open tennis tournament, Sunday, March 26, 2017, in Key Biscayne, Fla. (AP Photo/Luis M. Alvarez)

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Philipp Kohlschreiber, of Germany, returns the ball to Rafael Nadal, of Spain, during the Miami Open tennis tournament, Sunday, March 26, 2017, in Key Biscayne, Fla. (AP Photo/Luis M. Alvarez)

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Rafael Nadal, of Spain, returns the ball to Philipp Kohlschreiber, of Germany, during the Miami Open tennis tournament, Sunday, March 26, 2017, in Key Biscayne, Fla. (AP Photo/Luis M. Alvarez)

Philipp Kohlschreiber, of Germany, reacts after losing a point to Stanislas Wawrinka, of Switzerland, at the BNP Paribas Open tennis tournament, Monday, March 13, 2017, in Indian Wells, Calif. (AP Photo/Mark J. Terrill)

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Stanislas Wawrinka, of Switzerland, returns a shot to Philipp Kohlschreiber, of Germany, at the BNP Paribas Open tennis tournament, Monday, March 13, 2017, in Indian Wells, Calif. (AP Photo/Mark J. Terrill)

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John Isner, of the United States, reacts after a shot Philipp Kohlschreiber, of Germany, during the third round of the 2014 U.S. Open tennis tournament, Saturday, Aug. 30, 2014, in New York. (AP Photo/Darron Cummings)

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Germany's Philipp Kohlschreiber wipes his face as he plays Britain's Andy Murray during their third round match of the French Open tennis tournament at the Roland Garros stadium, in Paris, France, Sunday, June 1, 2014. Murray won 3-6, 6-3, 6-3, 4-6, 12-10. (AP Photo/Michel Spingler)