Stadium: Court 3 Round: 62 Ground: Clay
| ITF M25 Most | 2021/05/23 14:00 | Kai Lemstra v Vojtech Petr | 6-4,6-4 |
| ITF M25 Jablonec Nad Nisou | 2021/05/18 07:30 | Andrew Paulson v Kai Lemstra | 6-3,6-4 |
| ITF M25 Jablonec Nad Nisou | 2021/05/17 07:30 | Jan Jermar v Kai Lemstra | 4-6,4-6 |
| ITF M25 Jablonec Nad Nisou | 2021/05/16 08:30 | Matyas Cerny v Kai Lemstra | 3-6,3-6 |
| ITF M25 Meerbusch | 2021/04/12 09:30 | Marvin Netuschil v Kai Lemstra | 6-2,6-3 |
| ITF M15 Monastir | 2021/03/15 12:30 | Kai Lemstra v Alexander Kotzen | 1-6,3-6 |
| ITF M15 Monastir | 2021/03/15 08:00 | Kai Lemstra v John Sperle | 6-3,6-3 |
| ITF M15 Monastir | 2021/03/14 08:00 | Guy Orly Iradukunda v Kai Lemstra | 3-6,5-7 |
| ITF M25 Most | 2021/05/23 08:00 | Niklas Rohrer v Lukas Pokorny | 7-6,6-3 |
| ITF M25 Prague | 2021/05/09 13:30 | Lucas Bouquet v Niklas Rohrer | 6-1,6-3 |
| ITF M15 Antalya | 2021/04/11 07:00 | Marco De Rossi v Niklas Rohrer | 6-3,6-2 |
| ITF M15 Antalya | 2021/04/04 10:00 | Matteo Gigante v Niklas Rohrer | 6-2,6-0 |
| ITF M15 Antalya | 2021/03/28 06:30 | Andrea Borroni v Niklas Rohrer | 6-2,6-2 |
| ITF M15 Bratislava | 2021/03/09 09:00 | Niklas Rohrer v Stepan Pecak | 6-7,6-4,10-12 |
| ITF M15 Bratislava | 2021/03/01 12:00 | Jurgen Briand v Niklas Rohrer | 6-0,6-2 |
| ITF M15 Anif | 2020/08/23 07:00 | Kristof Minarik v Niklas Rohrer | 6-2,6-2 |