Jack Sock

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Jack Sock, of the United States, hits a backhand against Rafael Nadal, of Spain, during a quarterfinal match at the Miami Open tennis tournament, Wednesday, March 29, 2017, in Key Biscayne, Fla. (AP Photo/Mario Houben)

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Rafael Nadal, of Spain, plays a forehand against Jack Sock, of the United States, during a quarterfinal match at the Miami Open tennis tournament, Wednesday, March 29, 2017, in Key Biscayne, Fla. (AP Photo/Mario Houben)

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Roger Federer, of Switzerland, right, hugs Jack Sock after his win a semifinal match at the BNP Paribas Open tennis tournament, Saturday, March 18, 2017, in Indian Wells, Calif. (AP Photo/Mark J. Terrill)

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United States' Jack Sock hits to Roger Federer, of Switzerland, during a semifinal match at the BNP Paribas Open tennis tournament, Saturday, March 18, 2017, in Indian Wells, Calif. (AP Photo/Mark J. Terrill)

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Jack Sock hits to Roger Federer, of Switzerland during a semifinal match at the BNP Paribas Open tennis tournament, Saturday, March 18, 2017, in Indian Wells, Calif. (AP Photo/Mark J. Terrill)

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Roger Federer, of Switzerland, hits to Jack Sock during a semifinal match at the BNP Paribas Open tennis tournament, Saturday, March 18, 2017, in Indian Wells, Calif. (AP Photo/Mark J. Terrill)

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Roger Federer, of Switzerland, hits to Jack Sock during a semifinal match at the BNP Paribas Open tennis tournament, Saturday, March 18, 2017, in Indian Wells, Calif. (AP Photo/Mark J. Terrill)

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Jack Sock hits to Roger Federer, of Switzerland, during a semifinal match at the BNP Paribas Open tennis tournament, Saturday, March 18, 2017, in Indian Wells, Calif. (AP Photo/Mark J. Terrill)

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Kei Nishikori, of Japan, returns a shot to Jack Sock at the BNP Paribas Open tennis tournament, Friday, March 17, 2017, in Indian Wells, Calif. (AP Photo/Mark J. Terrill)

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Jack Sock returns a shot to Kei Nishikori, of Japan, at the BNP Paribas Open tennis tournament, Friday, March 17, 2017, in Indian Wells, Calif. (AP Photo/Mark J. Terrill)

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Kei Nishikori, of Japan, returns a shot to Jack Sock at the BNP Paribas Open tennis tournament, Friday, March 17, 2017, in Indian Wells, Calif. (AP Photo/Mark J. Terrill)

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Jack Sock returns a shot to Kei Nishikori, of Japan, at the BNP Paribas Open tennis tournament, Friday, March 17, 2017, in Indian Wells, Calif. (AP Photo/Mark J. Terrill)

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Jack Sock holds the championship trophy after Milos Raonic, of Canada withdrew from the tournament before the final match at the 2017 Delray Beach Open, Sunday, Feb. 26, 2017, in Delray Beach, Fla. (AP Photo/Joel Auerbach)

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Milos Raonic, of Canada,left, and Jack Sock, right, pose with their trophies after the 2017 Delray Beach Open, Sunday, Feb. 26, 2017, in Delray Beach, Fla. Jack Sock was awarded the championship after Milos Raonic withdrew prior to the start of the final match due to injury. (AP Photo/Joel Auerbach)