Angelique Kerber, of Germany, reacts after winning a match against Ann Li, off the United States, during the third round of the US Open tennis championships, Friday, Sept. 4, 2020, in New York. (AP Photo/Seth Wenig)

Naomi Osaka, of Japan, walks off the court after winning a match against Marta Kostyuk, of the Ukraine, during the third round of the US Open tennis championships, Friday, Sept. 4, 2020, in New York. (AP Photo/Seth Wenig)

David Goffin, of Belgium, returns a shot to Filip Krajinovic, of Serbia, during the third round of the US Open tennis championships, Friday, Sept. 4, 2020, in New York. (AP Photo/Seth Wenig)

Marta Kostyuk, of the Ukraine, returns a shot to Naomi Osaka, of Japan, during the third round of the US Open tennis championships, Friday, Sept. 4, 2020, in New York. (AP Photo/Seth Wenig)

Novak Djokovic, of Serbia, falls during a play against Jan-Lennard Struff, of Germany, during the third round of the U.S. Open tennis championships, Friday, Sept. 4, 2020, in New York. (AP Photo/Frank Franklin II)

Naomi Osaka, of Japan, returns a shot to Marta Kostyuk, of the Ukraine, during the third round of the US Open tennis championships, Friday, Sept. 4, 2020, in New York. (AP Photo/Seth Wenig)

Adrian Mannarino, of France, returns a shot to Jack Sock, of the United States, during the second round of the US Open tennis championships, Wednesday, Sept. 2, 2020, in New York. (AP Photo/Seth Wenig)

Ann Li, of the United States, returns a shot to Angelique Kerber, of Germany, during the third round of the US Open tennis championships, Friday, Sept. 4, 2020, in New York. (AP Photo/Seth Wenig)

Jennifer Brady, of the United States, returns a shot to Caroline Garcia, of France, during the third round of the US Open tennis championships, Friday, Sept. 4, 2020, in New York. (AP Photo/Seth Wenig)

Novak Djokovic, of Serbia, reacts to missing a point to Jan-Lennard Struff, of Germany, during the third round of the U.S. Open tennis championships, Friday, Sept. 4, 2020, in New York. (AP Photo/Frank Franklin II)

Petra Kvitova, of the Czech Republic, reacts to winning the match with Jessica Pegula, of the United States, during the third round of the U.S. Open tennis championships, Friday, Sept. 4, 2020, in New York. (AP Photo/Frank Franklin II)

Stefanos Tsitsipas, of Greece, returns a shot to Borna Coric, of Croatia, during the third round of the U.S. Open tennis championships, Friday, Sept. 4, 2020, in New York. (AP Photo/Frank Franklin II)

Borna Coric, of Croatia, returns a shot to Stefanos Tsitsipas, of Greece, during the third round of the U.S. Open tennis championships, Friday, Sept. 4, 2020, in New York. (AP Photo/Frank Franklin II)