| Champ: |  Marco Cecchinato |
| Score: | 6–2, 7–6(7–4) |
| Draw: | 28 (4 / 3) |
| Seeds: | 8 |
| Type: | singles doubles |
See main article: article and 2018 Croatia Open Umag.
Andrey Rublev was the defending champion, but lost in the quarterfinals to Robin Haase. This was Rublev's first tournament back on tour after missing three months due to a stress fracture in his back.[1]
Marco Cecchinato won the title, defeating Guido Pella in the final, 6–2, 7–6(7–4).
The top four seeds receive a bye into the second round.
