# 2021 Sparkassen Open – Singles

Thiago Monteiro was the defending champion but chose not to defend his title.
Daniel Altmaier won the title after defeating Henri Laaksonen 6–1, 6–2 in the final.

## Seeds

* Benoît Paire (second round)
* Ričardas Berankis (withdrew)
* Yannick Hanfmann (second round)
* Jozef Kovalík (quarterfinals)
* Henri Laaksonen (final)
* Tomáš Macháč (second round)
* Sumit Nagal (second round)
* Daniel Altmaier (champion)

## 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 |
| | Vít Kopřiva | 4 | 0 | | | | |
| 5 | Henri Laaksonen | 6 | 6 | | | | |
| 5 | Henri Laaksonen | 6 | 6 | 5 | Henri Laaksonen | 1 | 2 |
| | | | | 8 | Daniel Altmaier | 6 | 6 |
| 8 | Daniel Altmaier | 7 | 6 | 8 | Daniel Altmaier | 6 | 6 |
| WC | Marvin Möller | 5 | 0 | | | | |

### 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 |
| 1/WC | B Paire | 6 | 2 | 7 | | | | | | | | | | | | | | |
| | G Andreozzi | 4 | 6 | 5 | 1/WC | B Paire | 1 | 6 | 2 | | | | | | | | | |
| Q | D Michalski | 2 | 2 | | | V Kopřiva | 6 | 2 | 6 | | | | | | | | | |
| | V Kopřiva | 6 | 6 | | | | | | | | V Kopřiva | 3 | 6 | 7 | | | | |
| | Z Bergs | 6 | 6 | | | | | | | | Z Bergs | 6 | 0 | 5 | | | | |
| | M Marterer | 2 | 1 | | | Z Bergs | 7$^7$ | 5 | 6 | | | | | | | | | |
| | K Coppejans | 2 | 3 | | 6 | T Macháč | 6$^5$ | 7 | 4 | | | | | | | | | |
| 6 | T Macháč | 6 | 6 | | | | | | | | | | | | | V Kopřiva | 4 | 0 |
| 4 | J Kovalík | 7$^7$ | 6 | | | | | | | | | | | | 5 | H Laaksonen | 6 | 6 |
| | F Horanský | 6$^5$ | 3 | | 4 | J Kovalík | 6 | 7 | | | | | | | | | | |
| | A Vukic | 3 | 4 | | Alt | M Jaziri | 1 | 5 | | | | | | | | | | |
| Alt | M Jaziri | 6 | 6 | | | | | | | 4 | J Kovalík | 3 | 2 | | | | | |
| | N Kuhn | 6 | 7$^7$ | | | | | | | 5 | H Laaksonen | 6 | 6 | | | | | |
| Alt | M Zverev | 2 | 6$^4$ | | | N Kuhn | 4 | 5 | | | | | | | | | | |
| Q | M Rosenkranz | 3 | 2 | | 5 | H Laaksonen | 6 | 7 | | | | | | | | | | |
| 5 | H Laaksonen | 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 |
| 8 | D Altmaier | 6 | 7 | | | | | | | | | | | | | | |
| | Z Kolář | 2 | 5 | | 8 | D Altmaier | 6 | 6 | | | | | | | | | |
| | M Vilella Martínez | 3 | 6 | 6 | | M Vilella Martínez | 3 | 2 | | | | | | | | | |
| WC | R Molleker | 6 | 4 | 3 | | | | | | 8 | D Altmaier | 6 | 6 | | | | |
| | E Ymer | 6 | 7 | | | | | | | | E Ymer | 3 | 3 | | | | |
| | T Kamke | 3 | 5 | | | E Ymer | 2 | 6 | 6 | | | | | | | | |
| | S Diez | 5 | 6 | 3 | 3 | Y Hanfmann | 6 | 3 | 2 | | | | | | | | |
| 3 | Y Hanfmann | 7 | 2 | 6 | | | | | | | | | | 8 | D Altmaier | 7 | 6 |
| 7 | S Nagal | 6 | 7$^7$ | | | | | | | | | | | WC | M Möller | 5 | 0 |
| | M Safwat | 3 | 6$^3$ | | 7 | S Nagal | 3 | 6 | 2 | | | | | | | | |
| WC | M Möller | 7 | 6 | | WC | M Möller | 6 | 1 | 6 | | | | | | | | |
| | T Gabashvili | 5 | 3 | | | | | | | WC | M Möller | 6 | 6 | | | | |
| Q | S Ehrat | 6$^5$ | 6 | 6 | | | | | | LL | B Hassan | 4 | 2 | | | | |
| | M Moraing | 7$^7$ | 4 | 4 | Q | S Ehrat | 6 | 3 | 4 | | | | | | | | |
| LL | B Hassan | 6 | 7$^9$ | | LL | B Hassan | 4 | 6 | 6 | | | | | | | | |
| Q | D Kelly | 4 | 6$^7$ | | | | | | | | | | | | | | |