| UTR Pro Tennis Series Mulheim | 2021/07/30 13:30 | Guy Den Heijer v Alexander Hoogmartens | 6-2,3-6,4-6 |
| UTR Pro Tennis Series Mulheim | 2021/07/29 13:30 | Mark Wallner v Guy Den Heijer | 2-6,3-6 |
| UTR Pro Tennis Series Mulheim | 2021/07/29 07:00 | Matthew Thomson v Guy Den Heijer | 1-6,3-6 |
| UTR Pro Tennis Series Mulheim | 2021/07/27 09:30 | Billy Harris v Guy Den Heijer | 3-6,2-6 |
| UTR Pro Tennis Series Mulheim | 2021/07/26 11:00 | Guy Den Heijer v Tim Sandkaulen | 7-5,6-3 |
| ITF M25 Marburg | 2021/07/07 10:50 | Aleksandre Metreveli v Guy Den Heijer | 6-3,1-6,6-2 |
| ITF M25 Marburg | 2021/07/06 12:25 | Guy Den Heijer v Florian Broska | 6-3,7-6 |
| ITF M25 Marburg | 2021/07/05 08:00 | Guy Den Heijer v Maximilian Homberg | 6-7,6-2,10-8 |
| ITF M25 Alkmaar | 2021/06/20 12:00 | Jip Van Assendelft v Benjamin Dhoe | 2-6,3-6 |
| ITF M15 Antalya | 2021/05/30 07:30 | Jip Van Assendelft v Nicolas Agustin Lema | 4-6,7-6,10-12 |
| ITF M15 Antalya | 2021/05/24 10:00 | Jip Van Assendelft v Davide Albertoni | 2-6,1-6 |
| ITF M15 Antalya | 2021/05/23 07:00 | John Sperle v Jip Van Assendelft | 5-7,7-5,4-10 |
| ITF M15 Monastir | 2021/04/11 10:00 | Jip Van Assendelft v Piotr Matuszewski | 5-7,4-6 |
| ITF M15 Monastir | 2021/04/05 09:00 | Jip Van Assendelft v Romain Faucon | 3-6,6-1,7-10 |
| ITF M15 Monastir | 2021/04/04 10:30 | Justin Roberts v Jip Van Assendelft | 1-6,3-6 |
| ITF M25 Trimbach | 2021/03/08 13:35 | Patrik Hartmeier v Jip Van Assendelft | 7-5,7-5 |