2021 St. Petersburg Ladies' Trophy – Singles

Daria Kasatkina won the women's singles title at the 2021 St. Petersburg Ladies' Trophy, after Margarita Gasparyan retired from the final with the scoreline at 6–3, 2–1.

Kiki Bertens was the two-time defending champion, but she chose not to participate.

This was the first tournament since Oakland in 1993 in which seven of the eight quarterfinalists were all from the same country. It was also the first tournament in WTA history in which all four semifinalists represented Russia.

Seeds
• # 🇷🇺 Ekaterina Alexandrova (quarterfinals)

• # 🇷🇺 Veronika Kudermetova (quarterfinals)

• # 🇫🇷 Fiona Ferro (second round)

• # 🇷🇺 Svetlana Kuznetsova (semifinals)

• # 🇷🇺 Anastasia Pavlyuchenkova (second round)

• # Jeļena Ostapenko (second round)

• # 🇫🇷 Kristina Mladenovic (first round)

• # 🇷🇺 Daria Kasatkina (champion)

Seeds
• # Clara Tauson (qualified)

• # 🇧🇬 Viktoriya Tomova (moved to main draw)

• # 🇷🇴 Monica Niculescu (first round)

• # 🇷🇺 Natalia Vikhlyantseva (first round)

• # 🇷🇺 Kamilla Rakhimova (qualified)

• # 🇨🇳 Wang Xinyu (qualified)

• # 🇷🇴 Jaqueline Cristian (qualified)

• # 🇵🇱 Magdalena Fręch (qualifying competition)

• # 🇦🇺 Arina Rodionova (qualified)

• # 🇹🇷 Çağla Büyükakçay (qualifying competition, lucky loser)

• # Lesley Pattinama Kerkhove (qualifying competition)

• # 🇷🇴 Laura Ioana Paar (first round)

Qualifiers
• # Clara Tauson

• # 🇷🇴 Jaqueline Cristian

• # 🇷🇺 Anastasia Gasanova

• # 🇦🇺 Arina Rodionova

• # 🇷🇺 Kamilla Rakhimova

• # 🇨🇳 Wang Xinyu

Lucky loser
• # 🇹🇷 Çağla Büyükakçay