2021 Citi Open – Singles
| Singles | |
|---|---|
| 2021 Citi Open | |
| Champion | Jannik Sinner |
| Runner-up | Mackenzie McDonald |
| Score | 7–5, 4–6, 7–5 |
| Draw | 48 (6Q / 4WC) |
| Seeds | 16 |
Jannik Sinner defeated Mackenzie McDonald in the final, 7–5, 4–6, 7–5 to win the singles tennis title at the 2021 Citi Open. With the victory, Sinner became the youngest player and first teenager on the ATP Tour to win an ATP 500 title since the category was created in 2009.
Nick Kyrgios was the reigning champion from when the tournament was last held in 2019, but lost in the first round to McDonald.