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MELBOURNE, AUSTRALIA - JANUARY 17: Ivo Karlovic of Croatia serves in his second round match against Kei Nishikori of Japan during day four of the 2019 Australian Open at Melbourne Park on January 17, 2019 in Melbourne, Australia. (Photo by Michael Dodge/Getty Images)

MELBOURNE, AUSTRALIA - JANUARY 17:  Ivo Karlovic of Croatia serves in his second round match against Kei Nishikori of Japan during day four of the 2019 Australian Open at Melbourne Park on January 17, 2019 in Melbourne, Australia.  (Photo by Michael Dodge/Getty Images)