Novak Djokovic, right, and Nina Sojanovic, of Serbia, return to Luisa Stefani, bottom left, and Marcelo Melo, of Brazil, during a first round mixed doubles tennis match at the 2020 Summer Olympics, Wednesday, July 28, 2021, in Tokyo, Japan. (AP Photo/Patrick Semansky)

Novak Djokovic, right, and Nina Sojanovic, of Serbia, return to Luisa Stefani, bottom right, and Marcelo Melo, of Brazil, during a first round mixed doubles tennis match at the 2020 Summer Olympics, Wednesday, July 28, 2021, in Tokyo, Japan. (AP Photo/Patrick Semansky)

Novak Djokovic, top left, and Nina Sojanovic, of Serbia, prepare to return to Luisa Stefani, bottom left, and Marcelo Melo, of Brazil, during a first round mixed doubles tennis match at the 2020 Summer Olympics, Wednesday, July 28, 2021, in Tokyo, Japan. (AP Photo/Patrick Semansky)

Nina Sojanovic, left, and Novak Djokovic, of Serbia, high five during a first round mixed doubles tennis match against Luisa Stefani and Marcelo Melo, of Brazil, at the 2020 Summer Olympics, Wednesday, July 28, 2021, in Tokyo, Japan. (AP Photo/Patrick Semansky)