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Novak Djokovic of Serbia competes with Karen Khachanov of Russia during the 2018 Mubadala World Tennis Championship in Abu Dhabi, the United Arab Emirates (UAE), on Dec. 28, 2018. Novak Djokovic won 2-0. (Xinhua/Mahmoud Khaled)
Novak Djokovic of Serbia competes with Karen Khachanov of Russia during the 2018 Mubadala World Tennis Championship in Abu Dhabi, the United Arab Emirates (UAE), on Dec. 28, 2018. Novak Djokovic won 2-0. (Xinhua/Mahmoud Khaled)