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Nick Kyrgios of Australia serves during the men's singles fourth round match against Grigor Dimitrov of Bulgaria at Australian Open 2018 in Melbourne, Australia, Jan. 21, 2018. (Xinhua/Bai Xuefei)

Nick Kyrgios of Australia serves during the men's singles fourth round match against Grigor Dimitrov of Bulgaria at Australian Open 2018 in Melbourne, Australia, Jan. 21, 2018. (Xinhua/Bai Xuefei)