Stadium: M (CC) Round: 27 Ground: Clay
| UTR Pro Tennis Series Mulheim | 2021/07/30 13:30 | Guy Den Heijer v Alexander Hoogmartens | 6-2,3-6,4-6 |
| 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 |
| 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 |
| ITF M15 Oldenzaal | 2021/08/19 12:45 | Alexander Hoogmartens v Ryan Nijboer | 1-6,7-5,6-3 |
| ITF M15 Oldenzaal | 2021/08/18 07:55 | Alexander Hoogmartens v Deney Wassermann | 2-6,7-6,6-0 |
| UTR Pro Tennis Series Mulheim | 2021/07/31 08:30 | Vasile Antonescu v Alexander Hoogmartens | 5-7,7-6,6-1 |
| 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 | 2021/07/30 07:00 | Francesco Vilardo v Alexander Hoogmartens | 1-6,2-5 |
| UTR Pro Tennis Series Mulheim | 2021/07/29 08:30 | Jim Hendrikx v Alexander Hoogmartens | 4-6,3-6 |
| UTR Pro Tennis Series Mulheim | 2021/07/28 12:30 | Stefan Peter Hampe v Alexander Hoogmartens | 2-6,1-6 |
| UTR Pro Tennis Series Mulheim | 2021/07/26 08:00 | Hazem Naw v Alexander Hoogmartens | 6-4,5-4 |