2021 Serbia Open – Men's singles

Matteo Berrettini defeated Aslan Karatsev in the final, 6–1, 3–6, 7–6(7–0) to win the men's singles tennis title at the 2021 Serbia Open.

Andreas Seppi was the reigning champion from when the event was last held in 2012, but he decided not to participate this year.

Seeds
The top four seeds received a bye into the second round. • # 🇷🇸 Novak Djokovic (semifinals)

• # 🇮🇹 Matteo Berrettini (champion)

• # 🇷🇺 Aslan Karatsev (final)

• # 🇷🇸 Dušan Lajović (second round)

• # 🇷🇸 Filip Krajinović (quarterfinals)

• # 🇭🇺 Márton Fucsovics (withdrew)

• # 🇦🇺 John Millman (second round)

• # 🇷🇸 Miomir Kecmanović (quarterfinals)

• # 🇷🇸 Laslo Đere (first round)

Seeds
• # 🇮🇹 Gianluca Mager (qualified)

• # 🇦🇷 Facundo Bagnis (qualified)

• # 🇪🇸 Roberto Carballés Baena (qualifying competition, lucky loser)

• # João Sousa (qualifying competition, lucky loser)

• # 🇯🇵 Yūichi Sugita (first round)

• # 🇨🇴 Daniel Elahi Galán (first round)

• # 🇦🇷 Francisco Cerúndolo (qualified)

• # 🇯🇵 Taro Daniel (qualifying competition, lucky loser)

Qualifiers
• # 🇮🇹 Gianluca Mager

• # 🇦🇷 Facundo Bagnis

• # 🇦🇷 Francisco Cerúndolo

• # 🇫🇷 Arthur Rinderknech

Lucky losers
• # 🇪🇸 Roberto Carballés Baena

• # João Sousa

• # 🇯🇵 Taro Daniel