2021 Open de Oeiras IV – Singles

Carlos Alcaraz was the defending champion but chose not to defend his title.

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

Seeds
• # 🇫🇷 Mathias Bourgue (first round)

• # Wu Tung-lin (second round)

• # 🇩🇪 Julian Lenz (second round)

• # Tseng Chun-hsin (second round)

• # 🇪🇨 Roberto Quiroz (first round)

• # 🇪🇸 Carlos Gimeno Valero (quarterfinals)

• # 🇦🇷 Pedro Cachin (first round)

• # 🇮🇹 Riccardo Bonadio (second round)