2021 Croatia Open Umag – Singles
Dušan Lajović was the reigning champion from when the tournament was last held in 2019, but lost to Daniel Altmaier in the quarterfinals. Carlos Alcaraz won his maiden ATP Tour title, defeating Richard Gasquet in the final, 6–2, 6–2. With the victory, Alcaraz became the youngest player to win an ATP Tour title since Kei Nishikori at the 2008 Delray Beach International Tennis Championships. Seeds. The top four seeds receive a bye into the second round.