Stadium: M (CC) Round: 26 Ground: Clay
| ITF M15 Oldenzaal | 2021/08/18 08:00 | Simone Roncalli v Sander Jong | 4-6,3-6 |
| Challenger Amersfoort | 2021/07/12 09:00 | Sander Jong v Carlos Sanchez Jover | 6-1,6-4 |
| Challenger Amersfoort | 2021/07/11 10:00 | Eduard Esteve Lobato v Sander Jong | 2-6,5-7 |
| ITF M25 Haag | 2021/06/30 12:40 | Sander Jong v Jesper De Jong | 5-7,6-7 |
| ITF M25 Alkmaar | 2021/06/23 16:10 | Kai Wehnelt v Sander Jong | 6-2,7-6 |
| ITF M15 Alkmaar | 2020/08/24 08:00 | Martin Van Der Meerschen v Sander Jong | 6-3,7-6 |
| ITF M15 Alkmaar | 2020/08/23 08:00 | Sander Jong v Maxime Pauwels | 2-6,6-4,10-8 |
| ITF M15 Oldenzaal | 2021/08/18 12:35 | Vladimir Ivanov v Guy Den Heijer | 6-4,4-6,4-6 |
| ITF M15 Oldenzaal | 2021/08/17 09:15 | Guy Den Heijer v Alexis Canter | 6-4,6-4 |
| ITF M15 Oldenzaal | 2021/08/16 10:00 | Guy Den Heijer v Noel Larwig | 6-3,6-4 |
| ITF M15 Oldenzaal | 2021/08/15 14:00 | Guy Den Heijer v Paulo Knippling | 6-3,6-4 |
| 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 |