Stefanos Tsitsipas, of Greece, plays Frances Tiafoe, of the United States, during the second round of the tennis competition at the 2020 Summer Olympics, Tuesday, July 27, 2021, in Tokyo, Japan. (AP Photo/Seth Wenig)

Frances Tiafoe, of the United States, plays Stefanos Tsitsipas, of Greece, during the second round of the tennis competition at the 2020 Summer Olympics, Tuesday, July 27, 2021, in Tokyo, Japan. (AP Photo/Seth Wenig)

Stefanos Tsitsipas, of Greece, plays Frances Tiafoe, of the United States, during the second round of the tennis competition at the 2020 Summer Olympics, Tuesday, July 27, 2021, in Tokyo, Japan. (AP Photo/Seth Wenig)

Stefanos Tsitsipas, of Greece, pulls a thread off the net while playing Frances Tiafoe, of the United States, during the second round of the tennis competition at the 2020 Summer Olympics, Tuesday, July 27, 2021, in Tokyo, Japan. (AP Photo/Seth Wenig)

Stefanos Tsitsipas, right, of Greece, returns to Frances Tiafoe, of the United States, during second round of the men's tennis competition at the 2020 Summer Olympics, Tuesday, July 27, 2021, in Tokyo, Japan. (AP Photo/Patrick Semansky)

Stefanos Tsitsipas, of Greece, reacts after defeating Frances Tiafoe, of the United States, during the second round of the tennis competition at the 2020 Summer Olympics, Tuesday, July 27, 2021, in Tokyo, Japan. (AP Photo/Seth Wenig)

Frances Tiafoe, of the United States, prepares to serve to Stefanos Tsitsipas, of Greece, during second round of the men's tennis competition at the 2020 Summer Olympics, Tuesday, July 27, 2021, in Tokyo, Japan. (AP Photo/Patrick Semansky)

Frances Tiafoe, bottom, of the United States, returns to Stefanos Tsitsipas, of Greece, during second round of the men's tennis competition at the 2020 Summer Olympics, Tuesday, July 27, 2021, in Tokyo, Japan. (AP Photo/Patrick Semansky)

Stefanos Tsitsipas, of Greece, returns to Frances Tiafoe, of the United States, during second round of the men's tennis competition at the 2020 Summer Olympics, Tuesday, July 27, 2021, in Tokyo, Japan. (AP Photo/Patrick Semansky)

Frances Tiafoe, top, of the United States, attempts to return to Stefanos Tsitsipas, of Greece, during second round of the men's tennis competition at the 2020 Summer Olympics, Tuesday, July 27, 2021, in Tokyo, Japan. (AP Photo/Patrick Semansky)

Stefanos Tsitsipas, bottom, of Greece, returns to Frances Tiafoe, of the United States, during second round of the men's tennis competition at the 2020 Summer Olympics, Tuesday, July 27, 2021, in Tokyo, Japan. (AP Photo/Patrick Semansky)

Frances Tiafoe, of the United States, returns to Stefanos Tsitsipas, of Greece, during second round of the men's tennis competition at the 2020 Summer Olympics, Tuesday, July 27, 2021, in Tokyo, Japan. (AP Photo/Patrick Semansky)

Frances Tiafoe, of the United States, reacts while playing Stefanos Tsitsipas, of Greece, during the second round of the tennis competition at the 2020 Summer Olympics, Tuesday, July 27, 2021, in Tokyo, Japan. (AP Photo/Seth Wenig)

Frances Tiafoe, of the United States, returns to Stefanos Tsitsipas, of Greece, during second round of the men's tennis competition at the 2020 Summer Olympics, Tuesday, July 27, 2021, in Tokyo, Japan. (AP Photo/Patrick Semansky)