2021 Astana Open – Men's singles

John Millman was the defending champion, but lost in the quarterfinals to James Duckworth.

Kwon Soon-woo won his first ATP Tour title, defeating Duckworth in the final, 7–6(8–6), 6–3. Kwon became the first South Korean player to win a title at ATP Tour level since Lee Hyung-taik in the 2003 Sydney tournament.

Seeds
The top four seeds received a bye into the second round. • #🇷🇺 Aslan Karatsev (second round)

• #🇰🇿 Alexander Bublik (semifinals)

• #🇷🇸 Dušan Lajović (second round)

• #🇷🇸 Filip Krajinović (second round)

• #🇦🇺 John Millman (quarterfinals)

• #🇫🇷 Benoît Paire (first round)

• #🇷🇸 Laslo Đere (quarterfinals)

• #🇧🇾 Ilya Ivashka (semifinals)

Seeds
• # 🇦🇹 Jurij Rodionov (first round)

• # 🇺🇸 Maxime Cressy (qualifying competition)

• # 🇦🇺 Marc Polmans (qualified)

• # 🇷🇺 Evgeny Donskoy (qualified)

• # 🇺🇦 Illya Marchenko (first round)

• # 🇵🇱 Kacper Żuk (first round)

• # 🇸🇪 Elias Ymer (qualified)

• # 🇰🇿 Dmitry Popko (qualified)

Qualifiers
• # 🇰🇿 Dmitry Popko

• # 🇸🇪 Elias Ymer

• # 🇦🇺 Marc Polmans

• # 🇷🇺 Evgeny Donskoy