2021 İstanbul Cup – Singles

Sorana Cîrstea defeated Elise Mertens in the final, 6–1, 7–6(7–3) to win the women's singles tennis title at the 2021 İstanbul Cup. This was Cîrstea's first title since 2008. Cîrstea did not drop a set throughout the tournament.

Patricia Maria Țig was the defending champion, but she chose not to participate this year.

Seeds
• #🇧🇪 Elise Mertens (final)

• # Petra Martić (first round)

• #🇷🇺 Veronika Kudermetova (semifinals)

• #🇷🇺 Daria Kasatkina (second round)

• #🇨🇿 Barbora Krejčíková (second round)

• #🇷🇺 Anastasia Pavlyuchenkova (first round)

• #🇨🇳 Zheng Saisai (withdrew)

• #🇨🇳 Wang Qiang (second round)

Seeds
• # 🇫🇷 Océane Dodin (first round)

• # 🇷🇺 Kamilla Rakhimova (qualified)

• # 🇷🇴 Jaqueline Cristian (qualifying competition)

• # Leonie Küng (first round)

• # 🇦🇹 Barbara Haas (qualifying competition, lucky loser)

• # 🇫🇷 Harmony Tan (qualifying competition)

• # 🇪🇸 Nuria Párrizas Díaz (qualified)

• # 🇪🇸 Cristina Bucșa (qualified)

• # 🇪🇸 Lara Arruabarrena (qualified)

• # 🇷🇺 Anastasia Gasanova (qualified)

• # Mariam Bolkvadze (qualifying competition)

• # Liang En-shuo (first round)

Qualifiers
• # Tereza Mrdeža

• # 🇷🇺 Kamilla Rakhimova

• # 🇪🇸 Cristina Bucșa

• # 🇷🇺 Anastasia Gasanova

• # 🇪🇸 Nuria Párrizas Díaz

• # 🇪🇸 Lara Arruabarrena

Lucky loser
• # 🇦🇹 Barbara Haas