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AUCKLAND, NEW ZEALAND - JANUARY 10: Jack Sock of USA plays a forehand in his second round match against Peter Gojowczyk of Germany during day three of the ASB Men's Classic at ASB Tennis Centre on January 10, 2018 in Auckland, New Zealand. (Photo by Fiona Goodall/Getty Images)

AUCKLAND, NEW ZEALAND - JANUARY 10:  Jack Sock of USA plays a forehand in his second round match against Peter Gojowczyk of Germany during day three of the ASB Men's Classic at ASB Tennis Centre on January 10, 2018 in Auckland, New Zealand.  (Photo by Fiona Goodall/Getty Images)