Stadium: Court 2 Round: 62 Ground: Hardcourt outdoor
| ITF M15 Monastir | 2021/08/16 07:30 | Jeremy Beale v Lucca Pinto | 6-2,6-0 |
| ITF M15 Monastir | 2021/08/15 07:30 | Lucca Pinto v Masood Eisa-Beygi | 6-1,6-0 |
| ITF M15 Monastir | 2021/08/18 09:00 | Kai Lemstra v Duarte Vale | 4-6,3-6 |
| ITF M15 Monastir | 2021/08/17 07:30 | Federico Salomone v Kai Lemstra | 4-6,6-4,8-10 |
| ITF M15 Monastir | 2021/08/16 07:30 | Kai Lemstra v Blake Ellis | 6-4,6-3 |
| ITF M25 Wetzlar | 2021/08/02 14:00 | Osman Torski v Kai Lemstra | 6-4,0-6,10-5 |
| ITF M25 Most | 2021/05/26 10:15 | Antoine Escoffier v Kai Lemstra | 6-3,7-5 |
| ITF M25 Most | 2021/05/25 10:15 | Kai Lemstra v Edward Hubner | 6-1,6-1 |
| ITF M25 Most | 2021/05/24 08:00 | Kai Lemstra v Niklas Rohrer | 6-3,6-2 |
| ITF M25 Most | 2021/05/23 14:00 | Kai Lemstra v Vojtech Petr | 6-4,6-4 |