2021 Zagreb Open

Country	Player	Rank1	Seed
ARG	Federico Coria	92	1
ESP	Pedro Martínez	95	2
SVK	Andrej Martin	109	3
JPN	Yasutaka Uchiyama	110	4
POR	Pedro Sousa	113	5
FRA	Benjamin Bonzi	115	6
BIH	Damir Džumhur	118	7
BRA	Thiago Seyboth Wild	126	8

• Rankings are as of 3 May 2021.^[1]

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

• Sebastián Báez def. Juan Pablo Varillas 3–6, 6–3, 6–1.

• Evan King / Hunter Reese def. Andrey Golubev / Aleksandr Nedovyesov 6–2, 7–6^(7–4).