| UTR Pro Tennis Series Portoroz | 2021/08/29 09:30 | Rumler, Robert v Egor Agafonov | 7-6,6-1 |
| UTR Pro Tennis Series Portoroz | 2021/08/26 10:00 | Rumler, Robert v Gal Emersic Potocnik | 6-2,6-1 |
| UTR Pro Tennis Series Portoroz | 2021/08/26 07:00 | Rumler, Robert v Giacomo Revelli | 3-6,4-6 |
| UTR Pro Tennis Series Portoroz | 2021/08/25 07:00 | Rumler, Robert v Dahiya, Paras | 7-6,3-6,6-5 |
| Prostejov, Singles M-ITF-CZE-04A | 2021/08/17 07:55 | Rumler, Robert v Nick Chappell | 0-6,4-6 |
| ITF M25 Grodzisk Mazowiecki | 2021/08/04 15:30 | Rumler, Robert v Shintaro Mochizuki | 6-3,3-6,2-6 |
| ITF M25 Grodzisk Mazowiecki | 2021/08/02 14:10 | Rumler, Robert v Galus, Piotr | 7-5,7-6 |
| UTR Pro Tennis Series Copenhagen | 2021/06/14 08:00 | Rumler, Robert v Jorgensen, Sebastian Grundtvig | 0-0 |