| ITF M25 Eupen | 2021/09/09 09:00 | Romain Faucon v Guy Den Heijer | 6-4,6-4 |
| ITF M25 Eupen | 2021/09/08 07:30 | Guy Den Heijer v Kai Wehnelt | 3-6,6-3,6-2 |
| ITF M25 Eupen | 2021/09/07 10:05 | Guy Den Heijer v Tom Gentzsch | 6-3,6-4 |
| ITF M25 Eupen | 2021/09/06 14:45 | Guy Den Heijer v Yannick Lenaerts | 6-1,6-0 |
| ITF M15 Oldenzaal | 2021/08/21 10:10 | Guy Den Heijer v Damien Wenger | 4-6,2-6 |
| ITF M15 Oldenzaal | 2021/08/20 16:35 | Guy Den Heijer v Alexander Hoogmartens | 6-3,6-7,6-4 |
| ITF M15 Oldenzaal | 2021/08/20 10:20 | Sander Jong v Guy Den Heijer | 5-7,7-5,4-6 |
| ITF M15 Oldenzaal | 2021/08/18 12:35 | Vladimir Ivanov v Guy Den Heijer | 6-4,4-6,4-6 |
| UTR Pro Tennis Series Ricany | 2021/09/19 07:00 | Lawrence Bataljin v Stefanos Sakellaridis | 0-6,6-6 |
| UTR Pro Tennis Series Ricany | 2021/09/18 07:30 | Lawrence Bataljin v Michael Gloeckler | 6-4,5-2 |
| UTR Pro Tennis Series Ricany | 2021/09/11 12:00 | Lawrence Bataljin v Jiri Jenicek | 1-6,1-5 |
| UTR Pro Tennis Series Ricany | 2021/09/10 07:30 | Yanais Laurent v Lawrence Bataljin | 6-2,6-1 |
| UTR Pro Tennis Series Ricany | 2021/09/09 10:00 | Jan Satral v Lawrence Bataljin | 6-3,6-1 |
| UTR Pro Tennis Series Ricany | 2021/09/08 12:00 | Michalis Sakellaridis v Lawrence Bataljin | 2-6,3-5 |
| UTR Pro Tennis Series Ricany | 2021/09/06 12:00 | Andrey Chepelev v Lawrence Bataljin | 6-1,6-3 |
| UTR Pro Tennis Series Portoroz | 2021/08/21 11:00 | Lawrence Bataljin v Tilen Zitnik | 6-3,4-6,4-5 |