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, 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)

Emma Raducanu, of Great Britain, returns a shot to Belinda Bencic, of Switzerland, during the quarterfinals of the US Open tennis championships, Wednesday, Sept. 8, 2021, in New York. (AP Photo/Elise Amendola)

Karolina Pliskova, of the Czech Republic, eyes her return to Maria Sakkari, of Greece, during the quarterfinals of the U.S. Open tennis tournament Wednesday, Sept. 8, 2021, in New York. (AP Photo/Frank Franklin II)

Karolina Pliskova, of the Czech Republic, reacts after missing a shot to Maria Sakkari, of Greece, during the quarterfinals of the U.S. Open tennis tournament Wednesday, Sept. 8, 2021, in New York. (AP Photo/Frank Franklin II)

Maria Sakkari, of Greece, reacts after winning the first set against Karolina Pliskova, of the Czech Republic, during the quarterfinals of the U.S. Open tennis tournament Wednesday, Sept. 8, 2021, in New York. (AP Photo/Frank Franklin II)

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)

Emma Raducanu, of Great Britain, reacts after defeating Belinda Bencic, of Switzerland, during the quarterfinals of the US Open tennis championships, Wednesday, Sept. 8, 2021, in New York. (AP Photo/Elise Amendola)

Belinda Bencic, of Switzerland, returns a shot to Emma Raducanu, of Great Britain, during the quarterfinals of the US Open tennis championships, Wednesday, Sept. 8, 2021, in New York. (AP Photo/Elise Amendola)

Emma Raducanu, of Great Britain, returns a shot to Belinda Bencic, of Switzerland, during the quarterfinals of the US Open tennis championships, Wednesday, Sept. 8, 2021, in New York. (AP Photo/Elise Amendola)

Emma Raducanu, of Great Britain, reacts after defeating Belinda Bencic, of Switzerland, during the quarterfinals of the US Open tennis championships, Wednesday, Sept. 8, 2021, in New York. (AP Photo/Elise Amendola)

Emma Raducanu, of Great Britain, reacts after defeating Belinda Bencic, of Switzerland, during the quarterfinals of the US Open tennis championships, Wednesday, Sept. 8, 2021, in New York. (AP Photo/Elise Amendola)

Maria Sakkari, of Greece, hits a forehand to Karolina Pliskova, of the Czech Republic, during the quarterfinals of the U.S. Open tennis tournament Wednesday, Sept. 8, 2021, in New York. (AP Photo/Frank Franklin II)

Emma Raducanu, of Great Britain, reacts after defeating Belinda Bencic, of Switzerland, during the quarterfinals of the US Open tennis championships, Wednesday, Sept. 8, 2021, in New York. (AP Photo/Elise Amendola)