2021 St. Petersburg Open – Singles

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.

Seeds
The top four seeds received a bye into the second round. • #🇷🇺 Andrey Rublev (quarterfinals)

• #🇨🇦 Denis Shapovalov (quarterfinals)

• #🇪🇸 Roberto Bautista Agut (quarterfinals)

• #🇷🇺 Aslan Karatsev (second round)

• #🇺🇸 Taylor Fritz (final)

• #🇷🇺 Karen Khachanov (second round)

• #🇰🇿 Alexander Bublik (second round)

• #🇺🇸 Sebastian Korda (second round)

Seeds
• # Botic van de Zandschulp (qualified)

• # 🇫🇷 Benjamin Bonzi (first round)

• # 🇦🇷 Federico Coria (first round)

• # 🇷🇸 Miomir Kecmanović (qualifying competition)

• # 🇫🇮 Emil Ruusuvuori (qualified)

• # 🇯🇵 Yoshihito Nishioka (qualified)

• # 🇸🇪 Mikael Ymer (first round)

• # 🇧🇾 Egor Gerasimov (qualified)

Qualifiers
• # Botic van de Zandschulp

• # 🇫🇮 Emil Ruusuvuori

• # 🇧🇾 Egor Gerasimov

• # 🇯🇵 Yoshihito Nishioka