# 2021 Ostrava Challenger – Singles

Aslan Karatsev was the defending champion but chose not to defend his title.
Benjamin Bonzi won the title after defeating Renzo Olivo 6–4, 6–4 in the final.

## Seeds

* Grégoire Barrère (second round)
* Thiago Seyboth Wild (first round)
* Benjamin Bonzi (champion)
* Arthur Rinderknech (semifinals, retired)
* Marc Polmans (quarterfinals)
* Maxime Cressy (first round)
* Alejandro Tabilo (second round)
* Mohamed Safwat (first 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 |
| | Renzo Olivo | 5 | | | | | | |
| 4 | Arthur Rinderknech | 4$^r$ | | | | | | |
| 4 | Arthur Rinderknech | 4$^r$ | | | | Renzo Olivo | 4 | 4 |
| | | | | | 3 | Benjamin Bonzi | 6 | 6 |
| 3 | Benjamin Bonzi | 6 | 4 | 7$^7$ | 3 | Benjamin Bonzi | 6 | 6 |
| | Elias Ymer | 3 | 6 | 6$^5$ | | | | |

### 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 |
| 1 | G Barrère | 7$^{11}$ | 7 | | | | | | | | | | | | | | |
| Q | O Otte | 6$^9$ | 5 | | 1 | G Barrère | 6 | 4 | 3 | | | | | | | | |
| | Z Kolář | 6 | 4 | 2 | | TM Etcheverry | 3 | 6 | 6 | | | | | | | | |
| | TM Etcheverry | 1 | 6 | 6 | | | | | | | TM Etcheverry | 4 | 4 | | | | |
| Q | L Miedler | 3 | 6 | 4 | | | | | | | R Olivo | 6 | 6 | | | | |
| | R Olivo | 6 | 3 | 6 | | R Olivo | 6 | 6 | | | | | | | | | |
| | R Haase | 2 | 6 | 4 | 7 | A Tabilo | 2 | 3 | | | | | | | | | |
| 7 | A Tabilo | 6 | 4 | 6 | | | | | | | | | | | | R Olivo | 5 |
| 4 | A Rinderknech | 6 | 6 | | | | | | | | | | | | 4 | A Rinderknech | 4$^r$ |
| | M Bourgue | 4 | 0 | | 4 | A Rinderknech | 7 | 6 | | | | | | | | | |
| | B Schnur | 6 | 1 | 6 | | B Schnur | 5 | 4 | | | | | | | | | |
| Alt | MT Barrios Vera | 2 | 6 | 1 | | | | | | 4 | A Rinderknech | 3 | 6 | 6 | | | |
| | P Polansky | 3 | 5 | | | | | | | Q | L Klein | 6 | 3 | 4 | | | |
| Q | L Klein | 6 | 7 | | Q | L Klein | 7$^7$ | 4 | 6 | | | | | | | | |
| | L Rosol | 6$^4$ | 6 | 7 | | L Rosol | 6$^2$ | 6 | 2 | | | | | | | | |
| 8 | M Safwat | 7$^7$ | 2 | 5 | | | | | | | | | | | | | |

### 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 | Semifinals | Semifinals | Semifinals | Semifinals | Semifinals |
| 5 | M Polmans | 6 | 6 | | | | | | | | | | | | | | | |
| | B Kavčič | 3 | 3 | | 5 | M Polmans | 6 | 6 | | | | | | | | | | |
| | D Istomin | 0 | 6 | 6 | | D Istomin | 3 | 0 | | | | | | | | | | |
| | L Lacko | 6 | 1 | 4 | | | | | | 5 | M Polmans | 4 | 2 | | | | | |
| | C Lestienne | 2 | 0 | | | | | | | 3 | B Bonzi | 6 | 6 | | | | | |
| WC | J Lehečka | 6 | 6 | | WC | J Lehečka | 3 | 4 | | | | | | | | | | |
| | R Safiullin | 2 | 1 | | 3 | B Bonzi | 6 | 6 | | | | | | | | | | |
| 3 | B Bonzi | 6 | 6 | | | | | | | | | | | 3 | B Bonzi | 6 | 4 | 7$^7$ |
| 6 | M Cressy | 6 | 6$^5$ | 4 | | | | | | | | | | | E Ymer | 3 | 6 | 6$^5$ |
| | E Ymer | 3 | 7$^7$ | 6 | | E Ymer | 6 | 6 | | | | | | | | | | |
| WC | P Rikl | 4 | 2 | | | S Stakhovsky | 1 | 2 | | | | | | | | | | |
| | S Stakhovsky | 6 | 6 | | | | | | | | E Ymer | 7 | 6 | | | | | |
| | S Báez | 6 | 6 | | | | | | | Q | A Molčan | 5 | 3 | | | | | |
| WC | Martin Krumich | 2 | 2 | | | S Báez | 6 | 1 | 2$^r$ | | | | | | | | | |
| Q | A Molčan | 6 | 6 | | Q | A Molčan | 4 | 6 | 4 | | | | | | | | | |
| 2 | T Seyboth Wild | 1 | 4 | | | | | | | | | | | | | | | |