2021 Open de Oeiras – Singles

This was the first of four editions of the tournament in the 2021 ATP Challenger Tour calendar.

Zdeněk Kolář won the title after defeating Gastão Elias 6–4, 7–5 in the final.

Seeds
• # 🇩🇪 Oscar Otte (first round)

• # 🇫🇷 Enzo Couacaud (first round)

• # 🇮🇳 Ramkumar Ramanathan (withdrew)

• # 🇺🇸 Ernesto Escobedo (first round)

• # 🇦🇷 Andrea Collarini (first round)

• # 🇲🇦 Elliot Benchetrit (first round)

• # 🇮🇹 Gian Marco Moroni (second round)

• # 🇨🇿 Zdeněk Kolář (champion)