Holger Vitus Nodskov Rune of Denmark, reaches for a ball from Novak Djokovic, of Serbia, during the first round of the US Open tennis championships, Tuesday, Aug. 31, 2021, in New York. (AP Photo/Frank Franklin II)

Holger Vitus Nodskov Rune of Denmark, bottom, serves to Novak Djokovic, of Serbia, during the first round of the US Open tennis championships, Tuesday, Aug. 31, 2021, in New York. (AP Photo/Frank Franklin II)

Holger Vitus Nodskov Rune of Denmark, left, and Novak Djokovic, of Serbia, meet at the net after Djokovic won their first-round match at the US Open tennis championships, Tuesday, Aug. 31, 2021, in New York. (AP Photo/Frank Franklin II)