# 2021 Belgrade Challenger – Men's singles

This was the first of the three tournaments held in Belgrade for the 2021 tennis season. Belgrade also hosted a joint ATP/WTA tournament.
Roberto Carballés Baena won the title after defeating Damir Džumhur 6–4, 7–5 in the final.

## Seeds

* Roberto Carballés Baena (champion)
* Facundo Bagnis (quarterfinals)
* Daniel Elahi Galán (first round)
* Philipp Kohlschreiber (second round)
* Francisco Cerúndolo (first round)
* Taro Daniel (quarterfinals)
* Hugo Dellien (second round)
* Benjamin Bonzi (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 |
| 1 | Roberto Carballés Baena | 3 | 6 | 6 | | | | |
| | Liam Broady | 6 | 2 | 3 | | | | |
| | Liam Broady | 6 | 2 | 3 | 1 | Roberto Carballés Baena | 6 | 7 |
| | | | | | | Damir Džumhur | 4 | 5 |
| | Damir Džumhur | 3 | 6 | 6 | | Damir Džumhur | 4 | 5 |
| | Jozef Kovalík | 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 | Semifinals |
| 1 | R Carballés Baena | 6 | 7$^7$ | | | | | | | | | | | | | | | | |
| | A Rinderknech | 4 | 6$^4$ | | 1 | R Carballés Baena | 6 | 6 | | | | | | | | | | | |
| Q | M Trungelliti | 6 | 6 | | Q | M Trungelliti | 2 | 4 | | | | | | | | | | | |
| | D Petrović | 3 | 2 | | | | | | | 1 | R Carballés Baena | 7$^9$ | 6 | | | | | | |
| SE | B Rola | 6 | 2 | | | | | | | SE | B Rola | 6$^7$ | 1 | | | | | | |
| Q | A Giannessi | 4 | 0$^r$ | | SE | B Rola | 6 | 6 | | | | | | | | | | | |
| SE | G Oliveira | 0$^r$ | | | 8 | B Bonzi | 2 | 2 | | | | | | | | | | | |
| 8 | B Bonzi | 4 | | | | | | | | | | | | | 1 | R Carballés Baena | 3 | 6 | 6 |
| 3 | DE Galán | 5 | 6 | 4 | | | | | | | | | | | | L Broady | 6 | 2 | 3 |
| | S Ofner | 7 | 3 | 6 | | S Ofner | 6 | 1 | 5 | | | | | | | | | | |
| | L Broady | 6 | 6 | | | L Broady | 4 | 6 | 7 | | | | | | | | | | |
| | N Milojević | 3 | 4 | | | | | | | | L Broady | 6 | 6$^2$ | 6 | | | | | |
| | B Nakashima | 6$^7$ | 6 | 6 | | | | | | | B Nakashima | 4 | 7$^7$ | 4 | | | | | |
| Q | E Benchetrit | 7$^9$ | 1 | 0 | | B Nakashima | 6 | 6 | | | | | | | | | | | |
| | T Griekspoor | 6$^7$ | 4 | | 7 | H Dellien | 2 | 2 | | | | | | | | | | | |
| 7 | H Dellien | 7$^9$ | 6 | | | | | | | | | | | | | | | | |

### Bottom half

| First round | First round | First round | First round | First round | Second round | Second round | Second round | Second round | Quarterfinals | Quarterfinals | Quarterfinals | Quarterfinals | Quarterfinals | Semifinals | Semifinals | Semifinals | Semifinals |
| 6 | T Daniel | 6 | 7 | | | | | | | | | | | | | | |
| WC | M Miladinović | 1 | 5 | | 6 | T Daniel | 6 | 6 | | | | | | | | | |
| Q | M Bachinger | 7 | 4 | 0$^r$ | | A Hoang | 4 | 2 | | | | | | | | | |
| | A Hoang | 5 | 6 | 0 | | | | | 6 | T Daniel | 4 | 4 | | | | | |
| | D Džumhur | 4 | 6 | 6 | | | | | | D Džumhur | 6 | 6 | | | | | |
| WC | P Krstin | 6 | 2 | 3 | | D Džumhur | 6 | 6 | | | | | | | | | |
| | M Cressy | 5 | 6 | 2 | 4 | P Kohlschreiber | 4 | 3 | | | | | | | | | |
| 4 | P Kohlschreiber | 7 | 4 | 6 | | | | | | | | | | D Džumhur | 3 | 6 | 6 |
| 5 | F Cerúndolo | 6$^6$ | 1 | | | | | | | | | | | J Kovalík | 6 | 3 | 3 |
| | J Kovalík | 7$^8$ | 6 | | | J Kovalík | 6 | 7$^7$ | | | | | | | | | |
| | E Donskoy | 4 | 3 | | | F Gaio | 0 | 6$^4$ | | | | | | | | | |
| | F Gaio | 6 | 6 | | | | | | | J Kovalík | 2 | 6 | 6 | | | | |
| | O Otte | 3 | 6 | 3 | | | | | 2 | F Bagnis | 6 | 4 | 4 | | | | |
| WC | H Međedović | 6 | 1 | 6 | WC | H Međedović | 2 | 2 | | | | | | | | | |
| | J Rodionov | 6 | 1 | 2 | 2 | F Bagnis | 6 | 6 | | | | | | | | | |
| 2 | F Bagnis | 2 | 6 | 6 | | | | | | | | | | | | | |