Stadium: Court 7 Round: 27 Ground: Clay
| Challenger Braunschweig - MD | 2021/07/07 09:30 | Kolar/Olivetti v Hidalgo/Gornes | 7-5,6-7,8-10 |
| Challenger Braunschweig - MD | 2021/07/06 17:10 | Gabashvili/Kadhe v Sijsling/Smits | 4-6,5-7 |
| Challenger Forli - MD | 2021/06/15 14:20 | Lenz/Moraing v Sijsling/Smits | 4-6,7-6,10-1 |
| Challenger St. Petersburg - MD | 2021/03/11 11:00 | Sijsling/Smits v Kravchuk/Yevseyev | 2-6,4-6 |
| Challenger St. Petersburg - MD | 2021/03/10 10:00 | Gabashvili/Nedovyesov v Sijsling/Smits | 1-6,6-3,4-10 |
| Challenger Cherbourg - MD | 2021/02/11 14:45 | Sijsling/Smits v Klein/Molcan | 6-7,6-7 |
| Challenger Cherbourg - MD | 2021/02/09 14:45 | Drzewiecki/Jebavy v Sijsling/Smits | 6-1,6-7,7-10 |
| ITF - Bressuire M15 - MD | 2021/01/19 14:55 | de Schepper/Napolitano v Sijsling/Smits | 7-6,6-7,10-5 |
| ITF - Antalya M15 - MD | 2021/01/09 11:45 | Sijsling/Smits v Harris/Sabanin | 6-0,3-6,13-15 |