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Chung Hyeon of South Korea returns a shot during the men's singles fourth round match against Novak Djokovic of Serbia at Australian Open 2018 in Melbourne, Australia, Jan. 22, 2018. Chung Hyeon won by 3-0.(Xinhua/Bai Xuefei)

Chung Hyeon of South Korea returns a shot during the men's singles fourth round match against Novak Djokovic of Serbia at Australian Open 2018 in Melbourne, Australia, Jan. 22, 2018. Chung Hyeon won by 3-0.(Xinhua/Bai Xuefei)