Timo Boll of Germany competes during the men's singles round of 16 between Fan Zhendong of China and Timo Boll of Germany at the table tennis 2019 ITTF World Tour Grand Finals in Zhengzhou, central China's Henan Province, Dec. 12, 2019. (Photos: Xinhua)

Fan Zhendong of China serves during the men's singles round of 16 between Fan Zhendong of China and Timo Boll of Germany at the table tennis 2019 ITTF World Tour Grand Finals in Zhengzhou, central China's Henan Province, Dec. 12, 2019.

Fan Zhendong of China celebrates during the men's singles round of 16 between Fan Zhendong of China and Timo Boll of Germany at the table tennis 2019 ITTF World Tour Grand Finals in Zhengzhou, central China's Henan Province, Dec. 12, 2019.

Fan Zhendong of China competes during the men's singles round of 16 between Fan Zhendong of China and Timo Boll of Germany at the table tennis 2019 ITTF World Tour Grand Finals in Zhengzhou, central China's Henan Province, Dec. 12, 2019.

Timo Boll of Germany competes during the men's singles round of 16 between Fan Zhendong of China and Timo Boll of Germany at the table tennis 2019 ITTF World Tour Grand Finals in Zhengzhou, central China's Henan Province, Dec. 12, 2019.

Fan Zhendong of China serves during the men's singles round of 16 between Fan Zhendong of China and Timo Boll of Germany at the table tennis 2019 ITTF World Tour Grand Finals in Zhengzhou, central China's Henan Province, Dec. 12, 2019.

Lin Yun Ju of Chinese Taipei competes during the men's singles round of 16 match between Lin Yun Ju of Chinese Taipei and Mattias Falck of Sweden at the 2019 ITTF World Tour Grand Finals in Zhengzhou, central China's Henan Province, Dec. 12, 2019.

Mattias Falck of Sweden competes during the men's singles round of 16 match between Lin Yun Ju of Chinese Taipei and Mattias Falck of Sweden at the 2019 ITTF World Tour Grand Finals in Zhengzhou, central China's Henan Province, Dec. 12, 2019.

Lin Yun Ju of Chinese Taipei competes during the men's singles round of 16 match between Lin Yun Ju of Chinese Taipei and Mattias Falck of Sweden at the 2019 ITTF World Tour Grand Finals in Zhengzhou, central China's Henan Province, Dec. 12, 2019.

Liu Shiwen of China competes during the women's singles round of 16 between Liu Shiwen of China and Ishikawa Kasumi of Japan at the table tennis 2019 ITTF World Tour Grand Finals in Zhengzhou, central China's Henan Province, Dec. 12, 2019.

Ishikawa Kasumi of Japan competes during the women's singles round of 16 between Liu Shiwen of China and Ishikawa Kasumi of Japan at the table tennis 2019 ITTF World Tour Grand Finals in Zhengzhou, central China's Henan Province, Dec. 12, 2019.

Ishikawa Kasumi of Japan reacts during the women's singles round of 16 between Liu Shiwen of China and Ishikawa Kasumi of Japan at the table tennis 2019 ITTF World Tour Grand Finals in Zhengzhou, central China's Henan Province, Dec. 12, 2019.

Liu Shiwen of China competes during the women's singles round of 16 between Liu Shiwen of China and Ishikawa Kasumi of Japan at the table tennis 2019 ITTF World Tour Grand Finals in Zhengzhou, central China's Henan Province, Dec. 12, 2019.