Del Potro into US Open final after defending champion Nadal retires in semis

Rafael Nadal of Spain hits a return during the men's singles semifinal match against Juan Martin del Potro of Argentina at the 2018 US Open tennis tournament in New York, the United States, Sept. 7, 2018. Juan Martin del Potro won as Nadal retired due to injury. (Xinhua/Liu Jie)