| UTR Pro Tennis Series Mulheim | 2021/07/28 12:00 | Billy Harris v Matthew Thomson | 6-2,3-6,5-1 |
| UTR Pro Tennis Series Mulheim | 2021/07/27 09:30 | Mark Wallner v Matthew Thomson | 7-6,7-6 |
| 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 The Hague | 2021/06/29 15:00 | Dayne Kelly v Guy Den Heijer | 6-1,6-4 |
| ITF M25 The Hague | 2021/06/28 09:40 | Guy Den Heijer v Max Van Nunen | 6-3,6-1 |
| ITF M25 The Hague | 2021/06/27 08:00 | Guy Den Heijer v Jing L Weng | 6-3,6-4 |