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MELBOURNE, AUSTRALIA - JANUARY 28: Roger Federer of Switzerland plays a backhand during his Men’s Singles Quarterfinal match against Tennys Sandgren of the United States on day nine of the 2020 Australian Open at Melbourne Park on January 28, 2020 in Melbourne, Australia. (Photo by Mike Owen/Getty Images)

MELBOURNE, AUSTRALIA - JANUARY 28: Roger Federer of Switzerland plays a backhand during his Men’s Singles Quarterfinal match against Tennys Sandgren of the United States on day nine of the 2020 Australian Open at Melbourne Park on January 28, 2020 in Melbourne, Australia. (Photo by Mike Owen/Getty Images)