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ROME, ITALY - MAY 16: Kei Nishikori of Japan returns a forehand in his match against Grigor Dimitrov of Bulgaria during day 4 of the Internazionali BNL d'Italia 2018 tennis at Foro Italico on May 16, 2018 in Rome, Italy. (Photo by Dean Mouhtaropoulos/Getty Images)

ROME, ITALY - MAY 16:  Kei Nishikori of Japan returns a forehand in his match against Grigor Dimitrov of Bulgaria during day 4 of the Internazionali BNL d'Italia 2018 tennis at Foro Italico on May 16, 2018 in Rome, Italy.  (Photo by Dean Mouhtaropoulos/Getty Images)