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MELBOURNE, AUSTRALIA - JANUARY 24: Roger Federer of Switzerland serves in his quarterfinal match against Mischa Zverev of Germany on day nine of the 2017 Australian Open at Melbourne Park on January 24, 2017 in Melbourne, Australia. (Photo by Michael Dodge/Getty Images)

MELBOURNE, AUSTRALIA - JANUARY 24:  Roger Federer of Switzerland serves in his quarterfinal match against Mischa Zverev of Germany on day nine of the 2017 Australian Open at Melbourne Park on January 24, 2017 in Melbourne, Australia.  (Photo by Michael Dodge/Getty Images)