Stadium: Court 1 Round: 25 Ground: Hardcourt indoor
| Challenger Split Qual | 2021/04/11 10:25 | Mats Moraing v Lukas Klein | 6-4,3-6,3-6 |
| Challenger Bratislava | 2021/06/08 08:30 | Lukas Klein v Jiri Lehecka | 6-4,3-6,6-7 |
| ATP Belgrade | 2021/05/24 13:10 | Federico Delbonis v Lukas Klein | 3-6,6-3,6-4 |
| ATP Belgrade | 2021/05/23 10:25 | Christopher O'Connell v Lukas Klein | 7-6,7-5 |
| ATP Belgrade | 2021/05/22 10:35 | Marko Tepavac v Lukas Klein | 4-6,1-6 |
| Challenger Ostrava | 2021/04/30 10:40 | Arthur Rinderknech v Lukas Klein | 3-6,6-3,6-4 |
| Challenger Ostrava | 2021/04/28 09:00 | Lukas Klein v Lukas Rosol | 7-6,4-6,6-2 |
| Challenger Ostrava | 2021/04/27 10:00 | Peter Polansky v Lukas Klein | 3-6,5-7 |
| Challenger Ostrava | 2021/04/26 09:30 | Rudolf Molleker v Lukas Klein | 3-6,1-6 |
| Challenger Bratislava | 2021/06/07 14:00 | Mats Moraing v Martin Klizan | 6-7,7-6,5-7 |
| ATP Belgrade | 2021/05/25 12:00 | Novak Djokovic v Mats Moraing | 6-2,7-6 |
| ATP Belgrade | 2021/05/24 10:00 | Mats Moraing v Egor Gerasimov | 4-6,7-6,7-5 |
| ATP Belgrade | 2021/05/23 09:00 | Andrej Martin v Mats Moraing | 6-1,6-3 |
| ATP Belgrade | 2021/05/22 11:55 | Malek Jaziri v Mats Moraing | 3-6,4-6 |
| Challenger Oeiras | 2021/05/16 12:00 | Brayden Schnur v Mats Moraing | 6-4,6-4 |
| Challenger Heilbronn | 2021/05/12 14:10 | Dennis Novak v Mats Moraing | 7-6,4-6,7-5 |
| Challenger Heilbronn | 2021/05/11 12:20 | Mats Moraing v Henri Laaksonen | 7-6,6-2 |