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Novak Djokovic of Serbia returns the ball during the men's singles quarterfinals match against Kei Nishikori of Japan at 2019 Australian Open in Melbourne, Australia, Jan. 23, 2019. (Xinhua/Bai Xue)
Novak Djokovic of Serbia returns the ball during the men's singles quarterfinals match against Kei Nishikori of Japan at 2019 Australian Open in Melbourne, Australia, Jan. 23, 2019. (Xinhua/Bai Xue)