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MELBOURNE, AUSTRALIA - JANUARY 28: Stanislas Wawrinka of Switzerland watches on as Kei Nishikori of Japan leaves the court after Wawrink won their quarterfinal match during day 10 of the 2015 Australian Open at Melbourne Park on January 28, 2015 in Melbourne, Australia. (Photo by Clive Brunskill/Getty Images)

MELBOURNE, AUSTRALIA - JANUARY 28:  Stanislas Wawrinka of Switzerland watches on as Kei Nishikori of Japan leaves the court after Wawrink won their quarterfinal match during day 10 of the 2015 Australian Open at Melbourne Park on January 28, 2015 in Melbourne, Australia.  (Photo by Clive Brunskill/Getty Images)