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MELBOURNE, AUSTRALIA - JANUARY 20: Roger Federer of Switzerland plays a backhand in his fourth round match against Stefanos Tsitsipas of Greece during day seven of the 2019 Australian Open at Melbourne Park on January 20, 2019 in Melbourne, Australia. (Photo by Darrian Traynor/Getty Images)

MELBOURNE, AUSTRALIA - JANUARY 20:  Roger Federer of Switzerland plays a backhand in his fourth round match against Stefanos Tsitsipas of Greece during day seven of the 2019 Australian Open at Melbourne Park on January 20, 2019 in Melbourne, Australia.  (Photo by Darrian Traynor/Getty Images)