| 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 |
| ITF M25 Alkmaar | 2021/06/23 09:00 | Kaichi Uchida v Guy Den Heijer | 7-6,6-3 |
| ITF M25 Alkmaar | 2021/06/21 18:00 | Vladimir Ivanov v Guy Den Heijer | 3-6,6-7 |
| Challenger Braunschweig | 2021/07/05 09:30 | Tim Sandkaulen v Daniel Michalski | 3-6,5-7 |
| Challenger Braunschweig | 2021/07/04 09:00 | Kacper Zuk v Tim Sandkaulen | 6-2,3-6,6-7 |
| ITF USA F25 | 2018/09/15 17:30 | Alan Kohen v Tim Sandkaulen | 6-4,6-4 |
| ITF USA F25 | 2018/09/14 16:00 | Tim Sandkaulen v Robert Kelly | 6-7,6-1,6-0 |
| ITF Germany F9 | 2018/07/23 10:00 | Louroi Martinez v Tim Sandkaulen | 6-0,3-6,6-3 |
| ITF Germany F9 | 2018/07/22 11:00 | Tim Sandkaulen v Torben Steinorth | 6-4,6-1 |
| ITF Germany F9 | 2018/07/22 08:00 | Tim Sandkaulen v Lodewijk Weststrate | 6-2,7-6 |
| Challenger Meerbusch Qual | 2017/08/12 12:10 | Antonio Sancic v Tim Sandkaulen | 7-6,6-1 |