Stadium: Court 3 Round: 26 Ground: Clay
| ITF M15 Vejle | 2021/07/28 11:50 | Prechtel, Sebastian v Guy Den Ouden | 2-6,2-6 |
| ITF M15 Esch/Alzette | 2021/07/20 13:00 | von Der Schulenburg, Jeffrey v Guy Den Ouden | 6-4,3-6,7-5 |
| Challenger Amersfoort | 2021/07/11 14:00 | Guy Den Ouden v Hidalgo, Diego | 3-6,6-7 |
| ITF M25 Marburg | 2021/07/05 12:05 | Sabanin, Yan v Guy Den Ouden | 7-6,6-4 |
| ITF M25 The Hague | 2021/06/28 10:15 | Guy Den Ouden v Henri Squire | 2-6,0-6 |
| ITF M25 Alkmaar | 2021/06/23 10:35 | Deney Wassermann v Guy Den Ouden | 7-6,7-5 |
| ITF - M15 Sharm El Sheikh | 2020/11/19 10:10 | Guy Den Ouden v Miljan Zekic | 6-7,6-7 |
| ITF - M15 Sharm El Sheikh | 2020/11/18 12:45 | Juan Bautista Otegui v Guy Den Ouden | 6-1,3-6,4-6 |
| ITF M15 Vejle | 2021/07/28 12:45 | Gabriel Decamps v Veldheer, Mick | 3-6,1-6 |
| ITF M15 Esch/Alzette | 2021/07/22 09:55 | Nicholas David Ionel v Veldheer, Mick | 7-6,1-6,6-4 |
| ITF M15 Esch/Alzette | 2021/07/21 11:50 | Marlon Vankan v Veldheer, Mick | 3-6,6-0,6-7 |
| ITF M15 Esch/Alzette | 2021/07/20 15:50 | Kirill Kivattsev v Veldheer, Mick | 4-6,3-6 |
| ITF M25 Telfs | 2021/07/16 08:50 | Apostol, Bogdan Ionut v Veldheer, Mick | 6-4,5-7,7-5 |
| ITF M25 Telfs | 2021/07/13 09:20 | Veldheer, Mick v Alibek Kachmazov | 6-4,6-0 |
| ITF M25 The Hague | 2021/06/28 10:05 | Veldheer, Mick v Sidane Pontjodikromo | 5-7,3-6 |
| ITF M25 The Hague | 2021/06/27 08:00 | Veldheer, Mick v Jans, Jarno | 6-4,6-1 |