| UTR Pro Tennis Series Mulheim | 2021/09/21 08:00 | Colin Sinclair v Artem Podorozhnyi | 5-7,4-6 |
| UTR Pro Tennis Series Mulheim | 2021/09/20 09:30 | Colin Sinclair v Edison Ambarzumjan | 7-5,5-4 |
| Davis Cup | 2021/09/18 08:15 | Kareem Allaf v Colin Sinclair | 5-7,7-6,4-6 |
| Davis Cup | 2021/09/17 08:50 | Mousa Shanan Zayed v Colin Sinclair | 1-6,0-6 |
| Davis Cup | 2021/09/15 09:20 | Nam Hoang Ly v Colin Sinclair | 4-6,6-4,4-6 |
| ITF M25 Eupen | 2021/09/10 10:55 | Colin Sinclair v Facundo Diaz Acosta | 4-6,5-7 |
| ITF M25 Eupen | 2021/09/09 09:25 | Gauthier Onclin v Colin Sinclair | 6-2,2-6,4-6 |
| ITF M25 Eupen | 2021/09/08 09:30 | Colin Sinclair v Yan Sabanin | 6-3,7-6 |
| UTR Pro Tennis Series Mulheim | 2021/09/21 08:00 | Edison Ambarzumjan v Christos Keisidis | 6-2,4-6,5-1 |
| UTR Pro Tennis Series Sofia | 2021/09/03 07:00 | George Lazarov v Christos Keisidis | 6-4,6-4 |
| UTR Pro Tennis Series Sofia | 2021/09/02 07:00 | Vladimir Popov v Christos Keisidis | 7-6,6-7,3-6 |
| UTR Pro Tennis Series Sofia | 2021/09/01 08:00 | Christos Keisidis v Mario Radev | 6-1,4-6,6-4 |
| UTR Pro Tennis Series Sofia | 2021/08/31 08:00 | Christos Keisidis v Josh Sheehy | 4-6,4-6 |
| UTR Pro Tennis Series Sofia | 2021/08/30 07:00 | Christos Keisidis v Denislav Prodanov | 6-1,5-1 |
| ITF M15 Heraklion | 2021/06/09 08:00 | Antonio Cayetano March v Christos Keisidis | 4-6,7-6,6-2 |
| ITF M15 Heraklion | 2021/06/08 06:30 | Sean Hodkin v Christos Keisidis | 6-4,5-7,4-10 |