2021 Generali Open Kitzbühel – Singles

Miomir Kecmanović was the defending champion, but chose to compete at the Summer Olympics instead.

Casper Ruud won his fifth ATP Tour title, defeating Pedro Martínez in the final, 6–1, 4–6, 6–3. It was Ruud's third consecutive title in as many weeks.

Seeds
The top four seeds receive a bye into the second round. • # 🇳🇴 Casper Ruud (champion)

• # 🇪🇸 Roberto Bautista Agut (second round)

• # 🇷🇸 Filip Krajinović (quarterfinals)

• # 🇪🇸 Albert Ramos Viñolas (second round)

• # 🇦🇷 Federico Delbonis (first round)

• # 🇷🇸 Laslo Đere (first round)

• # Aljaž Bedene (withdrew)

• # 🇫🇷 Richard Gasquet (withdrew)

• # 🇪🇸 Jaume Munar (first round)

• # 🇪🇸 Carlos Alcaraz (first round)

Seeds
• # 🇪🇸 Carlos Taberner (qualifying competition, lucky loser)

• # 🇸🇰 Andrej Martin (qualifying competition)

• # 🇸🇰 Jozef Kovalík (qualified)

• # 🇦🇷 Juan Ignacio Londero (first round, retired)

• # 🇦🇷 Juan Manuel Cerúndolo (first round)

• # 🇦🇺 Marc Polmans (first round)

• # 🇷🇸 Nikola Milojević (first round)

• # 🇪🇸 Mario Vilella Martínez (qualifying competition, lucky loser)

Qualifiers
• # Ernests Gulbis

• # Holger Rune

• # 🇸🇰 Jozef Kovalík

• # 🇦🇹 Lukas Neumayer

Lucky losers
• # 🇪🇸 Carlos Taberner

• # 🇪🇸 Mario Vilella Martínez