# 2021 Brest Challenger – Singles

Ugo Humbert was the defending champion but chose not to defend his title.
Brandon Nakashima won the title after defeating João Sousa 6–3, 6–3 in the final.

## Seeds

* Arthur Rinderknech (first round)
* Jenson Brooksby (withdrew)
* Richard Gasquet (quarterfinals, withdrew)
* Brandon Nakashima (champion)
* Stefano Travaglia (second round)
* Pierre-Hugues Herbert (first round)
* Henri Laaksonen (quarterfinals)
* Hugo Gaston (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 | Final | Final | Final | Final |
| | Alexandre Müller | 2 | 5 | | | | |
| 4 | Brandon Nakashima | 6 | 7 | | | | |
| 4 | Brandon Nakashima | 6 | 7 | 4 | Brandon Nakashima | 6 | 6 |
| | | | | | João Sousa | 3 | 3 |
| Alt | Maxime Janvier | 5 | 1 | | João Sousa | 3 | 3 |
| | João Sousa | 7 | 6 | | | | |

### 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 | Semifinals | Semifinals | Semifinals | Semifinals |
| 1/WC | A Rinderknech | 4 | 2 | | | | | | | | | | | | | | |
| WC | M Guinard | 6 | 6 | | WC | M Guinard | 6$^4$ | 3 | | | | | | | | | |
| | F Horanský | 3 | 3 | | WC | L Van Assche | 7$^7$ | 6 | | | | | | | | | |
| WC | L Van Assche | 6 | 6 | | | | | | | WC | L Van Assche | 3 | 4 | | | | |
| Q | A Nedovyesov | 3 | 6 | 6$^2$ | | | | | | | A Müller | 6 | 6 | | | | |
| | A Müller | 6 | 3 | 7$^7$ | | A Müller | 7$^7$ | 1 | 6 | | | | | | | | |
| | M Safwat | 4 | 4 | | 5 | S Travaglia | 6$^4$ | 6 | 1 | | | | | | | | |
| 5 | S Travaglia | 6 | 6 | | | | | | | | | | | | A Müller | 2 | 5 |
| 4 | B Nakashima | 6 | 7$^7$ | | | | | | | | | | | 4 | B Nakashima | 6 | 7 |
| Q | Z Piros | 3 | 6$^4$ | | 4 | B Nakashima | 6 | 6 | | | | | | | | | |
| | F Verdasco | 6 | 4 | 1 | | B Zapata Miralles | 4 | 1 | | | | | | | | | |
| | B Zapata Miralles | 3 | 6 | 6 | | | | | | 4 | B Nakashima | 6 | 7 | | | | |
| | H Rune | 6 | 6 | | | | | | | 7 | H Laaksonen | 1 | 5 | | | | |
| | Z Kolář | 3 | 3 | | | H Rune | 4 | 4 | | | | | | | | | |
| | L Broady | 1 | 5 | | 7 | H Laaksonen | 6 | 6 | | | | | | | | | |
| 7 | H Laaksonen | 6 | 7 | | | | | | | | | | | | | | |

### Bottom 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 |
| 8 | H Gaston | 6 | 6 | | | | | | | | | | | | | | | |
| | S Caruso | 3 | 4 | | 8 | H Gaston | 6$^5$ | 6 | 4 | | | | | | | | | |
| LL | V Royer | 6 | 5 | 0 | Alt | M Janvier | 7$^7$ | 2 | 6 | | | | | | | | | |
| Alt | M Janvier | 3 | 7 | 6 | | | | | | Alt | M Janvier | w/o | | | | | | |
| | T Fabbiano | 7$^7$ | 7 | | | | | | | 3 | R Gasquet | | | | | | | |
| Q | A Vatutin | 6$^4$ | 5 | | | T Fabbiano | 2 | 6 | 2 | | | | | | | | | |
| | J Lehečka | 2 | 4 | | 3 | R Gasquet | 6 | 4 | 6 | | | | | | | | | |
| 3 | R Gasquet | 6 | 6 | | | | | | | | | | | | Alt | M Janvier | 5 | 1 |
| 6 | P-H Herbert | 4 | 6 | 3 | | | | | | | | | | | | J Sousa | 7 | 6 |
| | F Gaio | 6 | 3 | 6 | | F Gaio | 4 | 7$^7$ | 6 | | | | | | | | | |
| | F Ferreira Silva | 4 | 6 | 6 | | F Ferreira Silva | 6 | 6$^3$ | 2 | | | | | | | | | |
| | A Hoang | 6 | 4 | 4 | | | | | | | F Gaio | 3 | 7$^7$ | 6$^5$ | | | | |
| | J Sousa | 6 | 6 | | | | | | | | J Sousa | 6 | 6$^5$ | 7$^7$ | | | | |
| | H Grenier | 4 | 1 | | | J Sousa | 6 | 7$^8$ | | | | | | | | | | |
| SE | C Taberner | 6$^5$ | 6$^5$ | | Q | K de Schepper | 4 | 6$^6$ | | | | | | | | | | |
| Q | K de Schepper | 7$^7$ | 7$^7$ | | | | | | | | | | | | | | | |