
Roger Federer of Switzerland serves during the men's singles quarterfinal match against Florian Mayer of Germany in the Gerry Weber Open 2017 in Halle, Germany, on June 23, 2017. Roger Federer won 2-0. (Xinhua/Joachim Bywaletz)

Roger Federer of Switzerland serves during the men's singles quarterfinal match against Florian Mayer of Germany in the Gerry Weber Open 2017 in Halle, Germany, on June 23, 2017. Roger Federer won 2-0. (Xinhua/Joachim Bywaletz)