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Jack Sock of the US reacts after a point against Japan's Yuichi Sugata during their men's singles first round match on day one of the Australian Open tennis tournament in Melbourne on January 15, 2018. / AFP PHOTO / Paul Crock / -- IMAGE RESTRICTED TO EDITORIAL USE - STRICTLY NO COMMERCIAL USE -- (Photo credit should read PAUL CROCK/AFP/Getty Images)

Jack Sock of the US reacts after a point against Japan's Yuichi Sugata during their men's singles first round match on day one of the Australian Open tennis tournament in Melbourne on January 15, 2018. / AFP PHOTO / Paul Crock / -- IMAGE RESTRICTED TO EDITORIAL USE - STRICTLY NO COMMERCIAL USE --        (Photo credit should read PAUL CROCK/AFP/Getty Images)