| ITF M15 Monastir | 2021/08/26 07:30 | Kai Lemstra v Renta Tokuda | 2-6,2-6 |
| ITF M15 Monastir | 2021/08/25 07:30 | Hamzeh Al-Aswad v Kai Lemstra | 2-6,1-6 |
| ITF M15 Monastir | 2021/08/24 07:30 | Seita Watanabe v Kai Lemstra | 1-6,1-6 |
| ITF M15 Monastir | 2021/08/23 09:00 | Alec Beckley v Kai Lemstra | 3-6,2-6 |
| ITF M15 Monastir | 2021/08/22 12:00 | Lucca Pinto v Kai Lemstra | 3-6,0-6 |
| ITF M15 Monastir | 2021/08/18 09:00 | Kai Lemstra v Duarte Vale | 4-6,3-6 |
| ITF M15 Monastir | 2021/08/17 07:30 | Federico Salomone v Kai Lemstra | 4-6,6-4,8-10 |
| ITF M15 Monastir | 2021/08/16 07:30 | Kai Lemstra v Blake Ellis | 6-4,6-3 |
| 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 |
| Challenger Braunschweig | 2021/07/04 10:10 | Igor Sijsling v Diego Hidalgo | 3-6,6-3,4-6 |
| Challenger Forli | 2021/06/16 11:15 | Mats Moraing v Igor Sijsling | 3-6,6-4,6-2 |