# 2021 Swiss Open Gstaad – Singles

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.
Albert Ramos Viñolas was the reigning champion from when the tournament was last held in 2019, but chose to compete in Umag instead.

## Seeds

The top four seeds receive a bye into the second round.
* Denis Shapovalov (second round)
* Roberto Bautista Agut (second round)
* Casper Ruud (champion)
* Cristian Garín (quarterfinals)
* Federico Delbonis (second round)
* Benoît Paire (quarterfinals)
* Laslo Đere (semifinals)
* Feliciano López (second round)

## Draw
### Key

* Q = Qualifier
* WC = Wild card
* LL = Lucky loser
* Alt = Alternate
* SE = Special exempt
* PR = Protected ranking
* ITF = ITF entry
* JE = Junior exempt
* w/o = Walkover
* r = Retired
* d = Defaulted
* SR = Special ranking

### Finals

| Semifinals | Semifinals | Semifinals | Semifinals | Semifinals | Final | Final | Final | Final |
| Q | Vít Kopřiva | 3 | 0 | | | | | |
| 3 | Casper Ruud | 6 | 6 | | | | | |
| 3 | Casper Ruud | 6 | 6 | | 3 | Casper Ruud | 6 | 6 |
| | | | | | | Hugo Gaston | 3 | 2 |
| | Hugo Gaston | 3 | 6 | 6 | | Hugo Gaston | 3 | 2 |
| 7 | Laslo Đere | 6 | 3 | 3 | | | | |

### Top half

| First round | First round | First round | First round | First round | Second round | Second round | Second round | Second round | Second round | Quarterfinals | Quarterfinals | Quarterfinals | Quarterfinals | Quarterfinals | Semifinals | Semifinals | Semifinals | Semifinals |
| | | | | | 1 | D Shapovalov | 6 | 3 | 2 | | | | | | | | | |
| WC | J Nikles | 2 | 1 | | Q | V Kopřiva | 2 | 6 | 6 | | | | | | | | | |
| Q | V Kopřiva | 6 | 6 | | | | | | | Q | V Kopřiva | 6 | 6 | | | | | |
| | M Ymer | 4 | 6 | 6 | | | | | | | M Ymer | 1 | 0 | | | | | |
| LL | E Couacaud | 6 | 3 | 3 | | M Ymer | 6$^6$ | 7$^9$ | 6 | | | | | | | | | |
| | M-A Hüsler | 4 | 6 | 5$^r$ | 8 | F López | 7$^8$ | 6$^7$ | 4 | | | | | | | | | |
| 8 | F López | 6 | 4 | 6 | | | | | | | | | | | Q | V Kopřiva | 3 | 0 |
| | | | | | | | | | | | | | | | 3 | C Ruud | 6 | 6 |
| | | | | | 3 | C Ruud | 6 | 7$^7$ | | | | | | | | | | |
| LL | K Żuk | 4 | 4 | | | D Novak | 4 | 6$^5$ | | | | | | | | | | |
| | D Novak | 6 | 6 | | | | | | | 3 | C Ruud | 6 | 5 | 6 | | | | |
| | T Griekspoor | 7 | 4 | 7$^7$ | | | | | | 6 | B Paire | 2 | 7 | 3 | | | | |
| | JI Londero | 5 | 6 | 6$^1$ | | T Griekspoor | 4 | 0$^r$ | | | | | | | | | | |
| | J Kovalík | 3 | 6$^2$ | | 6 | B Paire | 6 | 0 | | | | | | | | | | |
| 6 | B Paire | 6 | 7$^7$ | | | | | | | | | | | | | | | |

### Bottom half

| First round | First round | First round | First round | Second round | Second round | Second round | Second round | Second round | Quarterfinals | Quarterfinals | Quarterfinals | Quarterfinals | Quarterfinals | Semifinals | Semifinals | Semifinals | Semifinals | Semifinals |
| 5 | F Delbonis | 6 | 6 | | | | | | | | | | | | | | | |
| WC | L Riedi | 3 | 3 | 5 | F Delbonis | 0 | 7$^7$ | 6$^3$ | | | | | | | | | | |
| | H Gaston | 6 | 6 | | H Gaston | 6 | 6$^2$ | 7$^7$ | | | | | | | | | | |
| | JM Cerúndolo | 4 | 2 | | | | | | | H Gaston | 6 | 1 | 7$^{13}$ | | | | | |
| | M Polmans | 7 | 6 | | | | | | 4 | C Garín | 4 | 6 | 6$^{11}$ | | | | | |
| Q | S Ehrat | 5 | 3 | | M Polmans | 3 | 0 | | | | | | | | | | | |
| | | | | 4 | C Garín | 6 | 6 | | | | | | | | | | | |
| | | | | | | | | | | | | | | | H Gaston | 3 | 6 | 6 |
| 7 | L Đere | 6 | 6 | | | | | | | | | | | 7 | L Đere | 6 | 3 | 3 |
| | T Seyboth Wild | 4 | 3 | 7 | L Đere | 6 | 4 | 6 | | | | | | | | | | |
| Q | O Otte | 6$^3$ | 1 | Q | Z Bergs | 2 | 6 | 2 | | | | | | | | | | |
| Q | Z Bergs | 7$^7$ | 6 | | | | | | 7 | L Đere | 6 | 6$^5$ | 6 | | | | | |
| | A Rinderknech | 6 | 6 | | | | | | | A Rinderknech | 4 | 7$^7$ | 4 | | | | | |
| WC | D Stricker | 4 | 4 | | A Rinderknech | 6 | 6 | | | | | | | | | | | |
| | | | | 2 | R Bautista Agut | 2 | 4 | | | | | | | | | | | |

## Qualifying
### Seeds

* Oscar Otte (qualified)
* Kacper Żuk (qualifying competition, lucky loser)
* Enzo Couacaud (qualifying competition, lucky loser)
* Steven Diez (qualifying competition)
* Ernests Gulbis (first round)
* Maximilian Marterer (first round)
* Aleksandar Vukic (first round)
* Roberto Marcora (qualifying competition)

### Qualifiers

* Oscar Otte
* Sandro Ehrat
* Vít Kopřiva
* Zizou Bergs

### Lucky losers

* Kacper Żuk
* Enzo Couacaud

### Qualifying draw
#### First qualifier

| First round | First round | First round | First round | First round | Qualifying competition | Qualifying competition | Qualifying competition | Qualifying competition |
| 1 | Oscar Otte | 6 | 6 | | | | | |
| | Andrea Pellegrino | 2 | 4 | | | | | |
| | Andrea Pellegrino | 2 | 4 | | 1 | Oscar Otte | 6 | 6 |
| | | | | | 8 | Roberto Marcora | 4 | 3 |
| Alt | Gonzalo Escobar | 6 | 4 | 6$^6$ | 8 | Roberto Marcora | 4 | 3 |
| 8 | Roberto Marcora | 1 | 6 | 7$^8$ | | | | |

#### Second qualifier

| First round | First round | First round | First round | First round | Qualifying competition | Qualifying competition | Qualifying competition | Qualifying competition | Qualifying competition |
| 2 | Kacper Żuk | 6 | 3 | 6 | | | | | |
| Alt | Andrea Vavassori | 3 | 6 | 2 | | | | | |
| Alt | Andrea Vavassori | 3 | 6 | 2 | 2 | Kacper Żuk | 6 | 4 | 2 |
| | | | | | WC | Sandro Ehrat | 2 | 6 | 6 |
| WC | Sandro Ehrat | 6 | 6 | | WC | Sandro Ehrat | 2 | 6 | 6 |
| 5 | Ernests Gulbis | 3 | 4 | | | | | | |

#### Third qualifier

| First round | First round | First round | First round | Qualifying competition | Qualifying competition | Qualifying competition | Qualifying competition | Qualifying competition |
| 3 | Enzo Couacaud | 6 | 6 | | | | | |
| | Pedro Sakamoto | 1 | 3 | | | | | |
| | Pedro Sakamoto | 1 | 3 | 3 | Enzo Couacaud | 6 | 6$^5$ | 4 |
| | | | | | Vít Kopřiva | 2 | 7$^7$ | 6 |
| | Vít Kopřiva | 6 | 6 | | Vít Kopřiva | 2 | 7$^7$ | 6 |
| 6 | Maximilian Marterer | 2 | 3 | | | | | |

#### Fourth qualifier

| First round | First round | First round | First round | Qualifying competition | Qualifying competition | Qualifying competition | Qualifying competition |
| 4 | Steven Diez | 6 | 6 | | | | |
| WC | Damien Wenger | 2 | 4 | | | | |
| WC | Damien Wenger | 2 | 4 | 4 | Steven Diez | 6$^5$ | 4 |
| | | | | | Zizou Bergs | 7$^7$ | 6 |
| | Zizou Bergs | 7$^7$ | 6 | | Zizou Bergs | 7$^7$ | 6 |
| 7 | Aleksandar Vukic | 6$^5$ | 3 | | | | |