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MELBOURNE, AUSTRALIA - JANUARY 16: Marin Cilic of Croatia plays a backhand in his second round match against Mackenzie Mcdonald of the United States during day three of the 2019 Australian Open at Melbourne Park on January 16, 2019 in Melbourne, Australia. (Photo by Julian Finney/Getty Images)

MELBOURNE, AUSTRALIA - JANUARY 16:  Marin Cilic of Croatia plays a backhand in his second round match against Mackenzie Mcdonald of the United States during day three of the 2019 Australian Open at Melbourne Park on January 16, 2019 in Melbourne, Australia.  (Photo by Julian Finney/Getty Images)