2021 Open de Oeiras III – Singles

Pedro Cachin was the defending champion but chose not to defend his title.

Carlos Alcaraz won the title after defeating Facundo Bagnis 6–4, 6–4 in the final.

Seeds
• # 🇨🇿 Jiří Veselý (second round, retired)

• # 🇺🇸 Steve Johnson (first round)

• # 🇦🇷 Federico Coria (second round)

• # 🇪🇸 Pedro Martínez (second round)

• # 🇩🇪 Yannick Hanfmann (first round)

• # 🇦🇷 Juan Ignacio Londero (first round)

• # 🇦🇷 Facundo Bagnis (final)

• # Pedro Sousa (quarterfinals)