2021 Stockholm Open – Singles

Tommy Paul defeated the defending champion, Denis Shapovalov, in the final, 6–4, 2–6, 6–4, to win the singles title at the 2021 Stockholm Open. This was Paul's first ATP Tour title.

Seeds
The top four seeds receive a bye into the second round. • #🇮🇹 Jannik Sinner (second round)

• #🇨🇦 Félix Auger-Aliassime (semifinals)

• #🇨🇦 Denis Shapovalov (final)

• #🇬🇧 Dan Evans (quarterfinals)

• #🇺🇸 Taylor Fritz (second round)

• #🇰🇿 Alexander Bublik (first round, retired)

• #🇭🇺 Márton Fucsovics (second round)

• #🇺🇸 Frances Tiafoe (semifinals)

Seeds
• # 🇧🇾 Egor Gerasimov (qualifying competition, lucky loser)

• # 🇸🇰 Jozef Kovalík (qualifying competition, lucky loser)

• # 🇷🇸 Nikola Milojević (first round)

• # 🇪🇬 Mohamed Safwat (first round)

• # Nino Serdarušić (qualifying competition, lucky loser)

• # 🇺🇿 Denis Istomin (qualified)

• # 🇷🇺 Teymuraz Gabashvili (first round)

• # 🇷🇺 Pavel Kotov (qualified)

Qualifiers
• # 🇷🇺 Pavel Kotov

• # 🇺🇿 Denis Istomin

• # 🇮🇹 Andrea Vavassori

• # 🇳🇴 Viktor Durasovic

Lucky losers
• # 🇧🇾 Egor Gerasimov

• # 🇸🇰 Jozef Kovalík

• # Nino Serdarušić