Yannick Hanfmann of Germany competes during the men's singles first round match with Rafael Nadal of Spain at French Open tennis tournament 2019 at Roland Garros, in Paris, France on May 27, 2019. (Photo: Xinhua/Han Yan)

Ground staff wipes the clay court during the break of the men's singles first round match between Rafael Nadal of Spain and Yannick Hanfmann of Germany at French Open tennis tournament 2019 at Roland Garros, in Paris, France on May 27, 2019. (Photo: Xinhua/Han Yan)

Rafael Nadal (L) of Spain and Yannick Hanfmann of Germany compete during their men's singles first round match at French Open tennis tournament 2019 at Roland Garros, in Paris, France on May 27, 2019. (Photo: Xinhua/Han Yan)

Rafael Nadal of Spain reacts during the men's singles first round match with Yannick Hanfmann of Germany at French Open tennis tournament 2019 at Roland Garros, in Paris, France on May 27, 2019. (Photo: Xinhua/Han Yan)

Rafael Nadal of Spain serves during the men's singles first round match with Yannick Hanfmann of Germany at French Open tennis tournament 2019 at Roland Garros, in Paris, France on May 27, 2019. (Photo: Xinhua/Han Yan)

Rafael Nadal of Spain returns the ball during the men's singles first round match with Yannick Hanfmann of Germany at French Open tennis tournament 2019 at Roland Garros, in Paris, France on May 27, 2019. (Photo: Xinhua/Han Yan)

Rafael Nadal of Spain returns the ball during the men's singles first round match with Yannick Hanfmann of Germany at French Open tennis tournament 2019 at Roland Garros, in Paris, France on May 27, 2019. (Photo: Xinhua/Han Yan)

Caroline Wozniacki of Denmark competes during the women's singles first round match with Veronica Kudermetova of Russia at French Open tennis tournament 2019 at Roland Garros in Paris, France on May 27, 2019. (Photo: Xinhua/Han Yan)

Caroline Wozniacki of Denmark competes during the women's singles first round match with Veronica Kudermetova of Russia at French Open tennis tournament 2019 at Roland Garros in Paris, France on May 27, 2019. (Photo: Xinhua/Han Yan)

Zhang Shuai of China returns the ball during the women's singles first round match with Varvara Lepchenko of the United States at French Open tennis tournament 2019 at Roland Garros in Paris, France on May 27, 2019. (Photo: Xinhua/Han Yan)

Zhang Shuai of China reacts during the women's singles first round match with Varvara Lepchenko of the United States at French Open tennis tournament 2019 at Roland Garros in Paris, France on May 27, 2019. (Photo: Xinhua/Han Yan)

Zhang Shuai of China returns the ball during the women's singles first round match with Varvara Lepchenko of the United States at French Open tennis tournament 2019 at Roland Garros in Paris, France on May 27, 2019. (Photo: Xinhua/Han Yan)

Caroline Wozniacki of Denmark competes during the women's singles first round match with Veronica Kudermetova of Russia at French Open tennis tournament 2019 at Roland Garros in Paris, France on May 27, 2019. (Photo: Xinhua/Han Yan)

Caroline Wozniacki of Denmark competes during the women's singles first round match with Veronica Kudermetova of Russia at French Open tennis tournament 2019 at Roland Garros in Paris, France on May 27, 2019. (Photo: Xinhua/Han Yan)

Caroline Wozniacki of Denmark serves during the women's singles first round match with Veronica Kudermetova of Russia at French Open tennis tournament 2019 at Roland Garros in Paris, France on May 27, 2019. (Photo: Xinhua/Han Yan)

Caroline Wozniacki of Denmark competes during the women's singles first round match with Veronica Kudermetova of Russia at French Open tennis tournament 2019 at Roland Garros in Paris, France on May 27, 2019. (Photo: Xinhua/Han Yan)

Caroline Wozniacki of Denmark competes during the women's singles first round match with Veronica Kudermetova of Russia at French Open tennis tournament 2019 at Roland Garros in Paris, France on May 27, 2019. (Photo: Xinhua/Han Yan)

Yannick Hanfmann of Germany competes during the men's singles first round match with Rafael Nadal of Spain at French Open tennis tournament 2019 at Roland Garros, in Paris, France on May 27, 2019. (Photo: Xinhua/Han Yan)

Yannick Hanfmann of Germany competes during the men's singles first round match with Rafael Nadal of Spain at French Open tennis tournament 2019 at Roland Garros, in Paris, France on May 27, 2019. (Photo: Xinhua/Han Yan)

Yannick Hanfmann of Germany competes during the men's singles first round match with Rafael Nadal of Spain at French Open tennis tournament 2019 at Roland Garros, in Paris, France on May 27, 2019. (Photo: Xinhua/Han Yan)

Zhang Shuai of China reacts during the women's singles first round match with Varvara Lepchenko of the United States at French Open tennis tournament 2019 at Roland Garros, in Paris, France on May 27, 2019. (Photo: Xinhua/Han Yan)

Zhang Shuai of China returns the ball during the women's singles first round match with Varvara Lepchenko of the United States at French Open tennis tournament 2019 at Roland Garros in Paris, France on May 27, 2019. (Photo: Xinhua/Han Yan)

Zhang Shuai of China reacts during the women's singles first round match with Varvara Lepchenko of the United States at French Open tennis tournament 2019 at Roland Garros, in Paris, France on May 27, 2019. (Photo: Xinhua/Han Yan)

Varvara Lepchenko of the United States competes during the women's singles first round match with Zhang Shuai of China at French Open tennis tournament 2019 at Roland Garros, in Paris, France on May 27, 2019. (Photo: Xinhua/Han Yan)