2021 Zagreb Open

The 2021 Zagreb Open was a professional tennis tournament played on clay courts. It was part of the 2021 ATP Challenger Tour. It took place in Zagreb, Croatia between 10 and 16 May 2021.

Seeds

 * Rankings are as of 3 May 2021.

Other entrants
The following players received wildcards into the singles main draw:
 * Borna Gojo
 * Nino Serdarušić
 * Antun Vidak

The following player received entry into the singles main draw as an alternate:
 * 🇰🇿 Dmitry Popko

The following players received entry from the qualifying draw:
 * 🇦🇷 Sebastián Báez
 * Marcelo Tomás Barrios Vera
 * Ernests Gulbis
 * 🇮🇳 Ramkumar Ramanathan

Singles

 * 🇦🇷 Sebastián Báez def. 🇵🇪 Juan Pablo Varillas 3–6, 6–3, 6–1.

Doubles

 * 🇺🇸 Evan King / 🇺🇸 Hunter Reese def. 🇰🇿 Andrey Golubev / 🇰🇿 Aleksandr Nedovyesov 6–2, 7–6(7–4).