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MELBOURNE, AUSTRALIA - JANUARY 20: Hyeon Chung of Korea serves in his third round match against Alexander Zverev of Germany on day six of the 2018 Australian Open at Melbourne Park on January 20, 2018 in Melbourne, Australia. (Photo by Scott Barbour/Getty Images)

MELBOURNE, AUSTRALIA - JANUARY 20:  Hyeon Chung of Korea serves in his third round match against Alexander Zverev of Germany on day six of the 2018 Australian Open at Melbourne Park on January 20, 2018 in Melbourne, Australia.  (Photo by Scott Barbour/Getty Images)