The U.S. Open took place from 8/29 to 11/9.
Djokovic was unable to enter the U.S. because he was unvaccinated, and Zverev has not fully recovered from his injury suffered at Roland Garros.
Defending champions Daniil Medvedev and Nick Kyrgios were in the spotlight on the opening day of the Grand Slam in New York today 29/8.
Medvedev began his campaign to defend the championship with a match against the host Stefan Kozlov.
The Russian had a difficult season, winning his first title in Los Cabos in early August.
Medvedev was then eliminated early in the Rogers Cup and reached the semifinals of the Cincinnati Masters.