Stadium: Court 6 Round: 44 Ground: Clay
| ITF M25 Jablonec Nad Nisou | 2021/05/16 08:30 | Jan Jermar v Peter Samosi | 7-6,6-0 |
| ITF M25 Prague | 2021/05/09 10:00 | Ondrej Horak v Jan Jermar | 7-6,6-3 |
| ITF M15 Las Palmas | 2021/04/25 11:00 | Jan Jermar v Xavier Gabarro | 0-6,2-6 |
| ITF M15 Sibenik | 2021/04/18 10:00 | Petr Hajek v Jan Jermar | 6-2,6-1 |
| ITF M15 Sharm El Sheikh | 2021/04/05 10:00 | Sean Hodkin v Jan Jermar | 7-5,6-2 |
| ITF M15 Sharm El Sheikh | 2021/04/04 07:30 | Shahar Gabay v Jan Jermar | 1-6,1-6 |
| ITF M15 Sharm El Sheikh | 2021/03/28 17:30 | Matej Galik v Jan Jermar | 6-0,6-1 |
| ITF M15 Sharm El Sheikh | 2021/03/22 11:30 | Jan Jermar v Sebastian Eguez | 5-7,7-6,8-10 |
| 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 M15 Monastir | 2021/03/11 10:40 | Kai Lemstra v Juan Bautista Torres | 4-6,1-6 |
| ITF M15 Monastir | 2021/03/10 12:15 | Kai Lemstra v Christoph Negritu | 6-4,2-6,6-1 |
| ITF M15 Monastir | 2021/03/08 18:00 | Anis Ghorbel v Kai Lemstra | 6-3,6-4 |