| Challenger Lisbon | 2021/09/27 15:10 | Igor Sijsling v Andrea Pellegrino | 0-6,4-6 |
| Challenger Braga | 2021/09/21 09:00 | Igor Sijsling v Michael Vrbensky | 1-6,4-6 |
| Challenger Prague | 2021/08/27 09:00 | Franco Agamenone v Igor Sijsling | 6-3,6-0 |
| Challenger Prague | 2021/08/26 10:00 | Igor Sijsling v Kaichi Uchida | 7-5,6-3 |
| Challenger Prague | 2021/08/24 13:45 | Daniel Siniakov v Igor Sijsling | 4-6,3-6 |
| Challenger Segovia | 2021/07/27 14:25 | Igor Sijsling v Teymuraz Gabashvili | 1-6,3-6 |
| Challenger Pozoblanco | 2021/07/22 16:00 | Tim Van Rijthoven v Igor Sijsling | 6-4,6-4 |
| Challenger Iasi | 2021/07/12 11:50 | Felipe Meligeni Rodrigues Alves v Igor Sijsling | 7-5,6-2 |
| Tie Break Tens Dubai | 2021/10/22 15:36 | Taylor Fritz v Simon Roberts | 1-0 |