Elina Svitolina of Ukraine celebrates winning the women's singles round robin match against Karolina Pliskova of the Czech Republic at the WTA finals Tennis Tournament in Shenzhen, south China's Guangdong Province on Oct. 28, 2019. (Xinhua/Liang Xu)

Elina Svitolina of Ukraine returns the ball during the women's singles round robin match against Karolina Pliskova of the Czech Republic at the WTA finals Tennis Tournament in Shenzhen, south China's Guangdong Province on Oct. 28, 2019. (Xinhua/Liang Xu)

Elina Svitolina of Ukraine returns the ball during the women's singles round robin match against Karolina Pliskova of the Czech Republic at the WTA finals Tennis Tournament in Shenzhen, south China's Guangdong Province on Oct. 28, 2019. (Xinhua/Liang Xu)

Elina Svitolina of Ukraine returns the ball during the women's singles round robin match against Karolina Pliskova of the Czech Republic at the WTA finals Tennis Tournament in Shenzhen, south China's Guangdong Province on Oct. 28, 2019. (Xinhua/Liang Xu)

Karolina Pliskova of the Czech Republic returns the ball during the women's singles round robin match against Elina Svitolina of Ukraine at the WTA finals Tennis Tournament in Shenzhen, south China's Guangdong Province on Oct. 28, 2019. (Xinhua/Liang Xu)

Karolina Pliskova of the Czech Republic returns the ball during the women's singles round robin match against Elina Svitolina of Ukraine at the WTA finals Tennis Tournament in Shenzhen, south China's Guangdong Province on Oct. 28, 2019. (Xinhua/Liang Xu)

Elina Svitolina of Ukraine returns the ball during the women's singles round robin match against Karolina Pliskova of the Czech Republic at the WTA finals Tennis Tournament in Shenzhen, south China's Guangdong Province on Oct. 28, 2019. (Xinhua/Liang Xu)

Karolina Pliskova of the Czech Republic reacts during the women's singles round robin match against Elina Svitolina of Ukraine at the WTA finals Tennis Tournament in Shenzhen, south China's Guangdong Province on Oct. 28, 2019. (Xinhua/Liang Xu)

Elina Svitolina of Ukraine celebrates winning the women's singles round robin match against Karolina Pliskova of the Czech Republic at the WTA finals Tennis Tournament in Shenzhen, south China's Guangdong Province on Oct. 28, 2019. (Xinhua/Liang Xu)

Elina Svitolina of Ukraine returns the ball during the women's singles round robin match against Karolina Pliskova of the Czech Republic at the WTA finals Tennis Tournament in Shenzhen, south China's Guangdong Province on Oct. 28, 2019. (Xinhua/Liang Xu)

Karolina Pliskova of the Czech Republic returns the ball during the women's singles round robin match against Elina Svitolina of Ukraine at the WTA finals Tennis Tournament in Shenzhen, south China's Guangdong Province on Oct. 28, 2019. (Xinhua/Liang Xu)

Elina Svitolina of Ukraine serves during the women's singles round robin match against Karolina Pliskova of the Czech Republic at the WTA finals Tennis Tournament in Shenzhen, south China's Guangdong Province on Oct. 28, 2019. (Xinhua/Liang Xu)

Elina Svitolina of Ukraine returns the ball during the women's singles round robin match against Karolina Pliskova of the Czech Republic at the WTA finals Tennis Tournament in Shenzhen, south China's Guangdong Province on Oct. 28, 2019. (Xinhua/Liang Xu)

Elina Svitolina of Ukraine returns the ball during the women's singles round robin match against Karolina Pliskova of the Czech Republic at the WTA finals Tennis Tournament in Shenzhen, south China's Guangdong Province on Oct. 28, 2019. (Xinhua/Liang Xu)

Elina Svitolina of Ukraine celebrates winning the women's singles round robin match against Karolina Pliskova of the Czech Republic at the WTA finals Tennis Tournament in Shenzhen, south China's Guangdong Province on Oct. 28, 2019. (Xinhua/Liang Xu)