# 2021 Dutch Open – Singles

Mats Moraing was the defending champion but lost in the second round to Botic van de Zandschulp.
Tallon Griekspoor won the title after defeating van de Zandschulp 6–1, 3–6, 6–1 in the final.

## Seeds

* Tallon Griekspoor (champion)
* Botic van de Zandschulp (final)
* Marc Polmans (first round)
* Antoine Hoang (semifinals)
* Mohamed Safwat (second round)
* Kimmer Coppejans (quarterfinals)
* Guido Andreozzi (semifinals)
* Lukáš Rosol (quarterfinals)

## 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 | Final |
| 1 | Tallon Griekspoor | 4 | 6 | 6 | | | | | |
| 4 | Antoine Hoang | 6 | 3 | 4 | | | | | |
| 4 | Antoine Hoang | 6 | 3 | 4 | 1 | Tallon Griekspoor | 6 | 3 | 6 |
| | | | | | 2 | Botic van de Zandschulp | 1 | 6 | 1 |
| 7 | Guido Andreozzi | 7$^7$ | 3 | 2 | 2 | Botic van de Zandschulp | 1 | 6 | 1 |
| 2 | Botic van de Zandschulp | 6$^4$ | 6 | 6 | | | | | |

### Top 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 | Semifinals |
| 1 | T Griekspoor | 6 | 7$^7$ | | | | | | | | | | | | | | | |
| Q | M Geerts | 2 | 6$^2$ | | 1 | T Griekspoor | 6 | 6 | | | | | | | | | | |
| | Z Bergs | 4 | 6$^2$ | | | M Vrbenský | 4 | 4 | | | | | | | | | | |
| | M Vrbenský | 6 | 7$^7$ | | | | | | 1 | T Griekspoor | 3 | 6 | 6 | | | | | |
| WC | G Brouwer | 7$^9$ | 0 | | | | | | 6 | K Coppejans | 6 | 3 | 2 | | | | | |
| Q | Alexander Maarten Jong | 6$^7$ | 0$^r$ | | WC | G Brouwer | 3 | 4 | | | | | | | | | | |
| Q | Deney Wassermann | 3 | 7 | 2 | 6 | K Coppejans | 6 | 6 | | | | | | | | | | |
| 6 | K Coppejans | 6 | 5 | 6 | | | | | | | | | | 1 | T Griekspoor | 4 | 6 | 6 |
| 4 | A Hoang | 6 | 7$^7$ | | | | | | | | | | | 4 | A Hoang | 6 | 3 | 4 |
| | Y Maden | 4 | 6$^5$ | | 4 | A Hoang | 7$^7$ | 7$^7$ | | | | | | | | | | |
| Alt | T Bellucci | 3 | 4 | | | F Mena | 6$^4$ | 6$^5$ | | | | | | | | | | |
| | F Mena | 6 | 6 | | | | | | 4 | A Hoang | 6 | 7$^7$ | | | | | | |
| WC | Ryan Nijboer | 6$^5$ | 2 | | | | | | 8 | L Rosol | 4 | 6$^4$ | | | | | | |
| Q | J Nikles | 7$^7$ | 6 | | Q | J Nikles | 2 | 1 | | | | | | | | | | |
| | V Kopřiva | 6$^4$ | 2 | | 8 | L Rosol | 6 | 6 | | | | | | | | | | |
| 8 | L Rosol | 7$^7$ | 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 | Quarterfinals | Semifinals | Semifinals | Semifinals | Semifinals | Semifinals |
| 7 | G Andreozzi | 7 | 2 | 6 | | | | | | | | | | | | | | | |
| | J Lehečka | 5 | 6 | 4 | 7 | G Andreozzi | 7 | 2 | 6 | | | | | | | | | | |
| | R Haase | 4 | 6$^1$ | | | A Vukic | 5 | 6 | 3 | | | | | | | | | | |
| | A Vukic | 6 | 7$^7$ | | | | | | | 7 | G Andreozzi | 3 | 6 | 6 | | | | | |
| | JC Aragone | 1 | 1 | | | | | | | WC | J Sels | 6 | 4 | 2 | | | | | |
| WC | J Sels | 6 | 6 | | WC | J Sels | 6 | 6 | | | | | | | | | | | |
| | A Vatutin | 6$^4$ | 6 | 6 | | A Vatutin | 2 | 2 | | | | | | | | | | | |
| 3 | M Polmans | 7$^7$ | 4 | 4 | | | | | | | | | | | 7 | G Andreozzi | 7$^7$ | 3 | 2 |
| 5 | M Safwat | 6 | 6 | | | | | | | | | | | | 2 | B van de Zandschulp | 6$^4$ | 6 | 6 |
| | G Elias | 1 | 3 | | 5 | M Safwat | 6 | 1 | 4 | | | | | | | | | | |
| | M Guinard | 6$^5$ | 6 | 6$^5$ | | J de Jong | 2 | 6 | 6 | | | | | | | | | | |
| | J de Jong | 7$^7$ | 4 | 7$^7$ | | | | | | | J de Jong | 3 | 0 | | | | | | |
| | M Moraing | 6 | 6 | | | | | | | 2 | B van de Zandschulp | 6 | 6 | | | | | | |
| Alt | J Härteis | 1 | 0 | | | M Moraing | 3 | 5 | | | | | | | | | | | |
| | G Oliveira | 2 | 4 | | 2 | B van de Zandschulp | 6 | 7 | | | | | | | | | | | |
| 2 | B van de Zandschulp | 6 | 6 | | | | | | | | | | | | | | | | |