| ITF M25 Belgrade | 2021/06/30 07:00 | Colin Sinclair v Edoardo Eremin | 2-6,1-6 |
| UTR Pro Tennis Series Bucharest | 2021/05/23 07:00 | Nicolae Frunza v Colin Sinclair | 5-6 |
| UTR Pro Tennis Series Bucharest | 2021/05/22 12:30 | Ilya Snitari v Colin Sinclair | 6-4,6-7,6-7 |
| UTR Pro Tennis Series Bucharest | 2021/05/22 07:00 | Colin Sinclair v Simon Beaupain | 6-3,6-4 |
| UTR Pro Tennis Series Bucharest | 2021/05/19 10:00 | Colin Sinclair v Juan Ignacio Galarza | 4-6,2-6 |
| UTR Pro Tennis Series Bucharest | 2021/05/18 10:00 | Colin Sinclair v Tomas Lipovsek Puches | 6-2,5-1 |
| UTR Pro Tennis Series Bucharest | 2021/05/17 12:30 | Nicholas David Ionel v Colin Sinclair | 6-7,4-5 |
| ITF M15 Antalya | 2021/05/10 07:00 | Colin Sinclair v Thomas Deschamps | 6-7,6-2,7-10 |
| 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 |
| ITF M25 Alkmaar | 2021/06/20 17:00 | Alec Deckers v Guy Den Heijer | 3-6,7-6,4-10 |
| ITF M25 Vic | 2021/05/16 08:00 | Mateus Alves v Guy Den Heijer | 6-2,6-3 |
| ITF M15 Valldoreix | 2021/05/09 13:00 | Guy Den Heijer v Pol Amoros Ramos | 3-6,2-6 |