# 2021 Belgrade Open – Singles

This was the first edition of the tournament, primarily created due to the one-week delay of the 2021 French Open.
Novak Djokovic won the title, defeating Alex Molčan in the final, 6–4, 6–3. It was Djokovic's third title ever in a tournament held in Serbia (excluding the Davis Cup).

## Seeds

The top four seeds receive a bye into the second round.
* Novak Djokovic (champion)
* Gaël Monfils (second round)
* Nikoloz Basilashvili (second round)
* Adrian Mannarino (second round)
* Dušan Lajović (quarterfinals)
* Filip Krajinović (withdrew)
* Miomir Kecmanović (first round)
* Federico Delbonis (semifinals)

## 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 | Novak Djokovic | 6 | 4 | 6 | | | | |
| Q | Andrej Martin | 1 | 6 | 0 | | | | |
| Q | Andrej Martin | 1 | 6 | 0 | 1 | Novak Djokovic | 6 | 6 |
| | | | | | Q | Alex Molčan | 4 | 3 |
| Q | Alex Molčan | 4 | 6 | 6 | Q | Alex Molčan | 4 | 3 |
| 8 | Federico Delbonis | 6 | 4 | 4 | | | | |

### 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 | N Djokovic | 6 | 7$^7$ | | | | | | | | | | | |
| LL | M Moraing | 4 | 7$^9$ | 7 | LL | M Moraing | 2 | 6$^4$ | | | | | | | | | | | |
| | E Gerasimov | 6 | 6$^7$ | 5 | | | | | | 1 | N Djokovic | 6 | 6 | | | | | | |
| WC | M Topo | 6 | 2 | 0 | | | | | | Alt | F Coria | 1 | 0 | | | | | | |
| Alt | F Coria | 4 | 6 | 6 | Alt | F Coria | 6 | 6 | | | | | | | | | | | |
| | P Cuevas | 6 | 6 | | | P Cuevas | 3 | 2 | | | | | | | | | | | |
| 7 | M Kecmanović | 3 | 2 | | | | | | | | | | | | 1 | N Djokovic | 6 | 4 | 6 |
| | | | | | | | | | | | | | | | Q | A Martin | 1 | 6 | 0 |
| | | | | | 3 | N Basilashvili | 1 | 6 | 6$^4$ | | | | | | | | | | |
| Q | C O'Connell | 6 | 6$^7$ | 5 | Q | A Martin | 6 | 4 | 7$^7$ | | | | | | | | | | |
| Q | A Martin | 3 | 7$^9$ | 7 | | | | | | Q | A Martin | 3 | 6 | 6 | | | | | |
| | T Sandgren | 4 | 2 | | | | | | | 5 | D Lajović | 6 | 3 | 4 | | | | | |
| | J Chardy | 6 | 6 | | | J Chardy | 3 | 4 | | | | | | | | | | | |
| | R Berankis | 3 | 3 | | 5 | D Lajović | 6 | 6 | | | | | | | | | | | |
| 5 | D Lajović | 6 | 6 | | | | | | | | | | | | | | | | |

### 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 |
| Q | A Molčan | 6 | 6 | | | | | | | | | | | | | | | |
| WC | H Međedović | 4 | 3 | | Q | A Molčan | 6 | 6 | | | | | | | | | | |
| WC | P Krstin | 6 | 3 | 6 | WC | P Krstin | 0 | 0 | | | | | | | | | | |
| | S-w Kwon | 2 | 6 | 1 | | | | | | Q | A Molčan | 6 | 6 | | | | | |
| | L Pouille | 5 | 2 | | | | | | | | F Verdasco | 2 | 0 | | | | | |
| | F Verdasco | 7 | 6 | | | F Verdasco | 7$^7$ | 6 | | | | | | | | | | |
| | | | | | 4 | A Mannarino | 6$^4$ | 0 | | | | | | | | | | |
| | | | | | | | | | | | | | | Q | A Molčan | 4 | 6 | 6 |
| 8 | F Delbonis | 3 | 6 | 6 | | | | | | | | | | 8 | F Delbonis | 6 | 4 | 4 |
| LL | L Klein | 6 | 3 | 4 | 8 | F Delbonis | 7$^8$ | 3 | 6 | | | | | | | | | |
| | R Albot | 2 | 2 | | | T Monteiro | 6$^6$ | 6 | 4 | | | | | | | | | |
| | T Monteiro | 6 | 6 | | | | | | | 8 | F Delbonis | w/o | | | | | | |
| SE | A Rinderknech | 0 | 4 | | | | | | | Q | R Carballés Baena | | | | | | | |
| Q | R Carballés Baena | 6 | 6 | | Q | R Carballés Baena | 6 | 3 | 7$^7$ | | | | | | | | | |
| | | | | | 2 | G Monfils | 1 | 6 | 6$^4$ | | | | | | | | | |

## Qualifying
### Seeds

* Federico Coria (moved to main draw)
* Roberto Carballés Baena (qualified)
* Andrej Martin (qualified)
* Christopher O'Connell (qualified)
* Mats Moraing (qualifying competition, lucky loser)
* Lukáš Klein (qualifying competition, lucky loser)
* Vít Kopřiva (qualifying competition)
* Alex Molčan (qualified)

### Qualifiers

* Alex Molčan
* Roberto Carballés Baena
* Andrej Martin
* Christopher O'Connell

### Lucky losers

* Mats Moraing
* Lukáš Klein

### Qualifying draw
#### First qualifier

| First round | First round | First round | First round | Qualifying competition | Qualifying competition | Qualifying competition | Qualifying competition |
| Alt | John-Patrick Smith | 4 | 6$^5$ | | | | |
| WC | Carlos Gómez-Herrera | 6 | 7$^7$ | | | | |
| WC | Carlos Gómez-Herrera | 6 | 7$^7$ | WC | Carlos Gómez-Herrera | 3 | 6$^8$ |
| | | | | 8 | Alex Molčan | 6 | 7$^{10}$ |
| Alt | Nerman Fatić | 4 | 1 | 8 | Alex Molčan | 6 | 7$^{10}$ |
| 8 | Alex Molčan | 6 | 6 | | | | |

#### Second qualifier

| First round | First round | First round | First round | First round | Qualifying competition | Qualifying competition | Qualifying competition | Qualifying competition |
| 2 | Roberto Carballés Baena | 6 | 6 | | | | | |
| | Mirza Bašić | 2 | 3 | | | | | |
| | Mirza Bašić | 2 | 3 | | 2 | Roberto Carballés Baena | 6 | 6 |
| | | | | | 7 | Vít Kopřiva | 4 | 4 |
| | Alexey Vatutin | 3 | 6 | 4 | 7 | Vít Kopřiva | 4 | 4 |
| 7 | Vít Kopřiva | 6 | 3 | 6 | | | | |

#### Third qualifier

| First round | First round | First round | First round | Qualifying competition | Qualifying competition | Qualifying competition | Qualifying competition |
| 3 | Andrej Martin | 6 | 6 | | | | |
| | Akira Santillan | 3 | 3 | | | | |
| | Akira Santillan | 3 | 3 | 3 | Andrej Martin | 6 | 6 |
| | | | | 5 | Mats Moraing | 1 | 3 |
| | Malek Jaziri | 3 | 4 | 5 | Mats Moraing | 1 | 3 |
| 5 | Mats Moraing | 6 | 6 | | | | |

#### Fourth qualifier

| First round | First round | First round | First round | Qualifying competition | Qualifying competition | Qualifying competition | Qualifying competition |
| 4 | Christopher O'Connell | 6 | 6 | | | | |
| | Darian King | 1 | 3 | | | | |
| | Darian King | 1 | 3 | 4 | Christopher O'Connell | 7$^9$ | 7 |
| | | | | 6 | Lukáš Klein | 6$^7$ | 5 |
| WC | Marko Tepavac | 4 | 1 | 6 | Lukáš Klein | 6$^7$ | 5 |
| 6 | Lukáš Klein | 6 | 6 | | | | |