Alexander Zverev, of Germany, left, greets Lloyd Harris, of South Africa, at the net after defeating Harris during the quarterfinals of the US Open tennis championships, Wednesday, Sept. 8, 2021, in New York. (AP Photo/Elise Amendola)

Alexander Zverev, of Germany, throws game balls to the crowd after defeating Lloyd Harris, of South Africa, during the quarterfinals of the US Open tennis championships, Wednesday, Sept. 8, 2021, in New York. (AP Photo/Elise Amendola)

Lloyd Harris, of South Africa, returns a shot to Alexander Zverev, of Germany, during the quarterfinals of the US Open tennis championships, Wednesday, Sept. 8, 2021, in New York. (AP Photo/Elise Amendola)

Alexander Zverev, of Germany, talks with court attendants as they dry liquid off the court during the quarterfinals of the US Open tennis championships against Lloyd Harris, of South Africa, Wednesday, Sept. 8, 2021, in New York. (AP Photo/Elise Amendola)

Lloyd Harris, of South Africa, returns a shot to Alexander Zverev, of Germany, during the quarterfinals of the US Open tennis championships, Wednesday, Sept. 8, 2021, in New York. (AP Photo/Elise Amendola)

Alexander Zverev, of Germany, returns a shot to Lloyd Harris, of South Africa, during the quarterfinals of the US Open tennis championships, Wednesday, Sept. 8, 2021, in New York. (AP Photo/Elise Amendola)