2021 St. Petersburg Open – Singles
| Singles | |
|---|---|
| 2021 St. Petersburg Open | |
| Champion | Marin Čilić |
| Runner-up | Taylor Fritz |
| Score | 7–6(7–3), 4–6, 6–4 |
| Draw | 28 (4 Q / 3 WC ) |
| Seeds | 8 |
Andrey Rublev was the defending champion, but lost in the quarterfinals to Botic van de Zandschulp.
Marin Čilić won the title, defeating Taylor Fritz in the final, 7–6(7–3), 4–6, 6–4.