Juan Martin del Potro beats John Isner at 2018 US Open men's singles quarterfinal match

Juan Martin del Potro of Argentina serves during the men's singles quarterfinal match against John Isner of the United States at the 2018 US Open in New York, the United States, Sept. 4, 2018. Juan Martin del Potro won 3-1. (Xinhua/Wang Ying)