The 2021 St. Petersburg Open was a tennis tournament played on indoor hard courts. It was the 26th edition of the St. Petersburg Open, and part of the ATP World Tour 250 Series of the 2021 ATP Tour. It took place at the Sibur Arena in Saint Petersburg, Russia, from October 25 through 31, 2021.[1]
See main article: 2021 St. Petersburg Open – Singles. Marin Čilić def. 
Taylor Fritz, 7–6(7–3), 4–6, 6–4
See main article: 2021 St. Petersburg Open – Doubles. 
Jamie Murray / 
Bruno Soares def. 
Andrey Golubev / Hugo Nys, 6–3, 6–4
| Country | Player | Rank1 | Seed | |
|---|---|---|---|---|
| Andrey Rublev | 6 | 1 | ||
| Denis Shapovalov | 14 | 2 | ||
| Roberto Bautista Agut | 20 | 3 | ||
| Aslan Karatsev | 22 | 4 | ||
| Taylor Fritz | 30 | 5 | ||
| Karen Khachanov | 31 | 6 | ||
| Alexander Bublik | 35 | 7 | ||
| Sebastian Korda | 38 | 8 |
The following players received wildcards into the singles main draw:
The following player received entry using a protected ranking:
The following players received entry from the qualifying draw:
| Country | Player | Country | Player | Rank1 | Seed | |
|---|---|---|---|---|---|---|
| United Kingdom | Jamie Murray | Brazil | Bruno Soares | 33 | 1 | |
| Raven Klaasen |  Japan | Ben McLachlan | 54 | 2 | ||
| Marcelo Arévalo | Matwé Middelkoop | 71 | 3 | |||
| Kazakhstan | Andrey Golubev | Hugo Nys | 87 | 4 |
The following pairs received wildcards into the doubles main draw:
