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MELBOURNE, AUSTRALIA - JANUARY 28: Stanislas Wawrinka of Switzerland serves in his quarterfinal match against Kei Nishikori of Japan during day 10 of the 2015 Australian Open at Melbourne Park on January 28, 2015 in Melbourne, Australia. (Photo by Cameron Spencer/Getty Images)

MELBOURNE, AUSTRALIA - JANUARY 28:  Stanislas Wawrinka of Switzerland serves in his quarterfinal match against Kei Nishikori of Japan during day 10 of the 2015 Australian Open at Melbourne Park on January 28, 2015 in Melbourne, Australia.  (Photo by Cameron Spencer/Getty Images)