see more

MELBOURNE, AUSTRALIA - JANUARY 15: Mitchell Krueger of the United States serves in his first round match against Novak Djokovic of Serbia during day two of the 2019 Australian Open at Melbourne Park on January 15, 2019 in Melbourne, Australia. (Photo by Julian Finney/Getty Images)

MELBOURNE, AUSTRALIA - JANUARY 15:  Mitchell Krueger of the United States serves in his first round match against Novak Djokovic of Serbia during day two of the 2019 Australian Open at Melbourne Park on January 15, 2019 in Melbourne, Australia.  (Photo by Julian Finney/Getty Images)