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MELBOURNE, AUSTRALIA - JANUARY 12: Kei Nishikori of Japan plays a backhand during a practice session ahead of the 2017 Australian Open at Melbourne Park on January 12, 2017 in Melbourne, Australia. (Photo by Scott Barbour/Getty Images)

MELBOURNE, AUSTRALIA - JANUARY 12:  Kei Nishikori of Japan plays a backhand during a practice session ahead of the 2017 Australian Open at Melbourne Park on January 12, 2017 in Melbourne, Australia.  (Photo by Scott Barbour/Getty Images)