Serena Williams of the United States hits a return during the women's singles third round match against Kristina Mladenovic of France at the Wimbledon Championships 2018 in London, Britain, on July 6, 2018. Serena Williams won 2-0. (Xinhua/Tang Shi)

Katarina Srebotnik (R) of Slovenia and Vania King of the United States compete during the women's doubles second round match against Han Xinyun of China and Luksika Kumkhum of Thailand at the Wimbledon Championships 2018 in London, Britain, on July 6, 2018. Katarina Srebotnik/Vania King won 2-1. (Xinhua/Guo Qiuda)

Kristina Mladenovic of France hits a return during the women's singles third round match against Serena Williams of the United States at the Wimbledon Championships 2018 in London, Britain, on July 6, 2018. Kristina Mladenovic lost 0-2. (Xinhua/Tang Shi)

Katarina Srebotnik (R) of Slovenia and Vania King of the United States compete during the women's doubles second round match against Han Xinyun of China and Luksika Kumkhum of Thailand at the Wimbledon Championships 2018 in London, Britain, on July 6, 2018. Katarina Srebotnik/Vania King won 2-1. (Xinhua/Guo Qiuda)

Roger Federer of Switzerland hits a return during the men's singles third round match against Jan-Lennard Struff of Germany at the Wimbledon Championships 2018 in London, Britain, on July 6, 2018. Roger Federer won 3-0. (Xinhua/Guo Qiuda)

Katarina Srebotnik (R) of Slovenia and Vania King of the United States compete during the women's doubles second round match against Han Xinyun of China and Luksika Kumkhum of Thailand at the Wimbledon Championships 2018 in London, Britain, on July 6, 2018. Katarina Srebotnik/Vania King won 2-1. (Xinhua/Guo Qiuda)

Han Xinyun (R) of China and Luksika Kumkhum of Thailand celebrate during the women's doubles second round match against Katarina Srebotnik of Slovenia and Vania King of the United States at the Wimbledon Championships 2018 in London, Britain, on July 6, 2018. Han Xinyun/Luksika Kumkhum lost 1-2. (Xinhua/Guo Qiuda)

Roger Federer of Switzerland greets spectators after the men's singles third round match against Jan-Lennard Struff of Germany at the Wimbledon Championships 2018 in London, Britain, on July 6, 2018. Roger Federer won 3-0. (Xinhua/Guo Qiuda)

Jan-Lennard Struff of Germany hits a return during the men's singles third round match against Roger Federer of Switzerland at the Wimbledon Championships 2018 in London, Britain, on July 6, 2018. Jan-Lennard Struff lost 0-3. (Xinhua/Guo Qiuda)

Han Xinyun (L) of China and Luksika Kumkhum of Thailand compete during the women's doubles second round match against Katarina Srebotnik of Slovenia and Vania King of the United States at the Wimbledon Championships 2018 in London, Britain, on July 6, 2018. Han Xinyun/Luksika Kumkhum lost 1-2. (Xinhua/Guo Qiuda)