Naomi Osaka, of Japan, serves 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)

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)

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)

Petra Kvitova, of the Czech Republic, reacts to winning a point to 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)

Novak Djokovic, of Serbia, returns a shot 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)

Taylor Fritz, of the United States, reacts during a match against Denis Shapovalov, of Canada, during the third round of the US Open tennis championships, Friday, Sept. 4, 2020, in New York. (AP Photo/Seth Wenig)

Alexander Zverev, of Germany, serves to Adrian Mannarino, of France, during the third round of the U.S. Open tennis championships, Friday, Sept. 4, 2020, in New York. (AP Photo/Frank Franklin II)

Adrian Mannarino, of France, returns a shot to Alexander Zverev, 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)

Denis Shapovalov, of Canada, reacts during a match against Taylor Fritz, of the United States, during the third round of the US Open tennis championships, Friday, Sept. 4, 2020, in New York. (AP Photo/Seth Wenig)

Caty McNally, of the United States, returns to Alize Cornet, France, at the Western & Southern Open tennis tournament, Saturday, Aug. 22, 2020, in New York. (AP Photo/Frank Franklin II)

Petra Martic, of Croatia, reacts during a match against Varvara Gracheva, of Russia, 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)

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

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