Zheng Saisai of China returns the ball during the women's singles first round between Zheng Saisai of China and Monica Puig of Puerto Rico at 2019 China Open tennis tournament in Beijing, capital of China, Sept. 28, 2019. (Xinhua/Jia Haocheng)

Monica Puig of Puerto Rico returns the ball during the women's singles first round between Zheng Saisai of China and Monica Puig of Puerto Rico at 2019 China Open tennis tournament in Beijing, capital of China, Sept. 28, 2019. (Xinhua/Jia Haocheng)

Zheng Saisai of China serves during the women's singles first round between Zheng Saisai of China and Monica Puig of Puerto Rico at 2019 China Open tennis tournament in Beijing, capital of China, Sept. 28, 2019. (Xinhua/Jia Haocheng)

Monica Puig of Puerto Rico returns the ball during the women's singles first round between Zheng Saisai of China and Monica Puig of Puerto Rico at 2019 China Open tennis tournament in Beijing, capital of China, Sept. 28, 2019. (Xinhua/Jia Haocheng)

Monica Puig of Puerto Rico returns the ball during the women's singles first round between Zheng Saisai of China and Monica Puig of Puerto Rico at 2019 China Open tennis tournament in Beijing, capital of China, Sept. 28, 2019. (Xinhua/Jia Haocheng)