| Champ: |  Casper Ruud |
| Runner: |  Hugo Gaston |
| Score: | 6–3, 6–2 |
| Draw: | 28 (4 / 3) |
| Seeds: | 8 |
| Type: | singles doubles |
| Before Year: | 2019 |
See main article: article and 2021 Swiss Open Gstaad.
Casper Ruud defeated Hugo Gaston in the final, 6–3, 6–2, to win the men's singles tennis title at the 2021 Swiss Open.[1]
Albert Ramos Viñolas was the reigning champion from when the tournament was last held in 2019, but chose to compete in Umag instead.
The top four seeds receive a bye into the second round.