Alexander Zverev of Germany hits a return during the men's singles first round match against Oscar Otte of Germany at the French Open tennis tournament at Roland Garros in Paris, France, May 30, 2021. (Photos: Aurelien Morissard/Xinhua)

Alexander Zverev of Germany hits a return during the men's singles first round match against Oscar Otte of Germany at the French Open tennis tournament at Roland Garros in Paris, France, May 30, 2021.

Oscar Otte of Germany hits a return during the men's singles first round match against Alexander Zverev of Germany at the French Open tennis tournament at Roland Garros in Paris, France, May 30, 2021.

Alexander Zverev of Germany hits a return during the men's singles first round match against Oscar Otte of Germany at the French Open tennis tournament at Roland Garros in Paris, France, May 30, 2021.

Oscar Otte of Germany hits a return during the men's singles first round match against Alexander Zverev of Germany at the French Open tennis tournament at Roland Garros in Paris, France, May 30, 2021.

Stefanos Tsitsipas of Greece hits a return during the men's singles first round match against Jeremy Chardy of France at the French Open tennis tournament at Roland Garros in Paris, France, May 30, 2021.

Jeremy Chardy of France hits a return during the men's singles first round match against Stefanos Tsitsipas of Greece at the French Open tennis tournament at Roland Garros in Paris, France, May 30, 2021.

Pablo Andujar of Spain hits a return during the men's singles first round match against Dominic Thiem of Austria at the French Open tennis tournament at Roland Garros in Paris, France, May 30, 2021.

Stefanos Tsitsipas of Greece hits a return during the men's singles first round match against Jeremy Chardy of France at the French Open tennis tournament at Roland Garros in Paris, France, May 30, 2021.

Dominic Thiem of Austria hits a return during the men's singles first round match against Pablo Andujar of Spain at the French Open tennis tournament at Roland Garros in Paris, France, May 30, 2021.