Catherine McNally, of the United States, returns a shot to Karolina Pliskova, of the Czech Republic, during the first round of the US Open tennis championships, Tuesday, Aug. 31, 2021, in New York. (AP Photo/John Minchillo)

Novak Djokovic, of Serbia, returns a shot during the first round of the US Open tennis championships, Tuesday, Aug. 31, 2021, in New York. (AP Photo/Frank Franklin II)

Tennis fans watch play between Karolina Pliskova, of the Czech Republic, and Catherine McNally, of the United States, during the first round of the US Open tennis championships, Tuesday, Aug. 31, 2021, in New York. (AP Photo/John Minchillo)

Karolina Pliskova, of the Czech Republic, prepares for a serve from Catherine McNally, of the United States, during the first round of the US Open tennis championships, Tuesday, Aug. 31, 2021, in New York. (AP Photo/John Minchillo)

Karolina Pliskova, of the Czech Republic, serves to Catherine McNally, of the United States, during the first round of the US Open tennis championships, Tuesday, Aug. 31, 2021, in New York. (AP Photo/John Minchillo)

Novak Djokovic, of Serbia, returns a shot during the first round of the US Open tennis championships, Tuesday, Aug. 31, 2021, in New York. (AP Photo/Frank Franklin II)

Karolina Pliskova, of the Czech Republic, serves to Catherine McNally, of the United States, during the first round of the US Open tennis championships, Tuesday, Aug. 31, 2021, in New York. (AP Photo/John Minchillo)

Taylor Fritz, of the United States, returns the ball during the first round of the US Open tennis championships, Tuesday, Aug. 31, 2021, in New York. (AP Photo/Frank Franklin II)

Ashleigh Barty, of Australia, returns a shot to Vera Zvonareva, of Russia, during the first round of the US Open tennis championships, Tuesday, Aug. 31, 2021, in New York. (AP Photo/John Minchillo)

Jenson Brooksby, of the United States, serves the ball during the first round of the US Open tennis championships, Tuesday, Aug. 31, 2021, in New York. (AP Photo/Elise Amendola)

Ashleigh Barty, of Australia, serves to Vera Zvonareva, of Russia, during the first round of the US Open tennis championships, Tuesday, Aug. 31, 2021, in New York. (AP Photo/John Minchillo)

Alexander Zverev, of Germany, serves to Sam Querrey, of the United States, during the first round of the US Open tennis championships, Tuesday, Aug. 31, 2021, in New York. (AP Photo/John Minchillo)

Alexander Zverev, of Germany, serves to Sam Querrey, of the United States, during the first round of the US Open tennis championships, Tuesday, Aug. 31, 2021, in New York. (AP Photo/John Minchillo)

Maxime Cressy, of the United States, returns a shot to Pablo Carreno Busta, of Spain, during the first round of the US Open tennis championships, Tuesday, Aug. 31, 2021, in New York. (AP Photo/Seth Wenig)

Bianca Andreescu, of Canada, waits for a trainer at a break during the first round of the US Open tennis championships, Tuesday, Aug. 31, 2021, in New York. (AP Photo/Frank Franklin II)

Alexander Zverev, of Germany, returns a shot to Sam Querrey, of the United States, during the first round of the US Open tennis championships, Tuesday, Aug. 31, 2021, in New York. (AP Photo/John Minchillo)

Ashleigh Barty, of Australia, serves to Vera Zvonareva, of Russia, during the first round of the US Open tennis championships, Tuesday, Aug. 31, 2021, in New York. (AP Photo/John Minchillo)