2021 Kremlin Cup – Men's singles
| Men's singles | |
|---|---|
| 2021 Kremlin Cup | |
| Champion | Aslan Karatsev |
| Runner-up | Marin Čilić |
| Score | 6–2, 6–4 |
| Draw | 28 (4 Q / 3 WC ) |
| Seeds | 8 |
Andrey Rublev was the reigning champion from when the tournament was last held in 2019, but lost to Adrian Mannarino in the second round in a rematch of the 2019 final.
Aslan Karatsev won the title, defeating Marin Čilić in the final, 6–2, 6–4.