Novak Djokovic, of Serbia, celebrates after defeating Kei Nishikori, of Japan, during the quarterfinals of the tennis competition at the 2020 Summer Olympics, Thursday, July 29, 2021, in Tokyo, Japan. (AP Photo/Seth Wenig)

Daniil Medvedev, of the Russian Olympic Committee, returns to Pablo Carreno Busta, of Spain, during the quarterfinal round of the men's tennis competition at the 2020 Summer Olympics, Thursday, July 29, 2021, in Tokyo, Japan. (AP Photo/Patrick Semansky)

Novak Djokovic, of Serbia, celebrates after defeating Kei Nishikori, of Japan, during the quarterfinals of the tennis competition at the 2020 Summer Olympics, Thursday, July 29, 2021, in Tokyo, Japan. (AP Photo/Seth Wenig)

Kei Nishikori, of Japan, reacts while playing Novak Djokovic, of Serbia, during the quarterfinals of the tennis competition at the 2020 Summer Olympics, Thursday, July 29, 2021, in Tokyo, Japan. (AP Photo/Seth Wenig)

The Serbian mixed doubles team of Nina Stojanovic, left, and Novak Djokovic play during the quarterfinals of the tennis competition at the 2020 Summer Olympics, Thursday, July 29, 2021, in Tokyo, Japan. (AP Photo/Seth Wenig)

Pablo Carreno Busta, of Spain, returns to Daniil Medvedev, of the Russian Olympic Committee, during the quarterfinal round of the men's tennis competition at the 2020 Summer Olympics, Thursday, July 29, 2021, in Tokyo, Japan. (AP Photo/Patrick Semansky)

Marketa Vondrousova, of the Czech Republic, plays Elina Svitolina, of the Ukraine, during the semifinals of the tennis competition at the 2020 Summer Olympics, Thursday, July 29, 2021, in Tokyo, Japan. (AP Photo/Seth Wenig)

Karen Khachanov, of the Russian Olympic Committee, wipes sweat from his brow during a quarterfinal men's tennis match against Ugo Humbert, of France, at the 2020 Summer Olympics, Thursday, July 29, 2021, in Tokyo, Japan. (AP Photo/Patrick Semansky)

Belinda Bencic, of Switzerland, plays Elena Rybakina, of Kazakhstan, during the semifinals of the tennis competition at the 2020 Summer Olympics, Thursday, July 29, 2021, in Tokyo, Japan. (AP Photo/Seth Wenig)

Kei Nishikori, of Japan, rests between points while playing Novak Djokovic, of Serbia, during the quarterfinals of the tennis competition at the 2020 Summer Olympics, Thursday, July 29, 2021, in Tokyo, Japan. (AP Photo/Seth Wenig)

Belinda Bencic, of Switzerland, reacts after defeating Elena Rybakina, of Kazakhstan, during the semifinals of the tennis competition at the 2020 Summer Olympics, Thursday, July 29, 2021, in Tokyo, Japan. (AP Photo/Seth Wenig)

Novak Djokovic, of Serbia, plays Kei Nishikori, of Japan, during the quarterfinals of the tennis competition at the 2020 Summer Olympics, Thursday, July 29, 2021, in Tokyo, Japan. (AP Photo/Seth Wenig)

Belinda Bencic, of Switzerland, becomes emotional after defeating Elena Rybakina, of Kazakhstan, during the semifinals of the tennis competition at the 2020 Summer Olympics, Thursday, July 29, 2021, in Tokyo, Japan. (AP Photo/Seth Wenig)