Stadium: Court 1 Round: 25 Ground: Clay
| ITF M25 Wetzlar | 2021/08/06 15:55 | Constantin Schmitz v Peter Heller | 3-6,7-5,1-6 |
| ITF M25 Wetzlar | 2021/08/05 13:55 | Dayne Kelly v Constantin Schmitz | 2-6,1-6 |
| ITF M25 Wetzlar | 2021/08/04 12:30 | Constantin Schmitz v Jannik Rother | 6-2,6-0 |
| ITF M15 Troisdorf | 2021/05/12 09:00 | Constantin Schmitz v Tom Kocevar-Desman | 6-4,4-6,3-6 |
| ITF M15 Antalya | 2021/04/14 10:30 | Ivan Sergeyev v Constantin Schmitz | 6-3,5-7,6-3 |
| ITF M15 Antalya | 2021/04/08 06:55 | Flavio Cobolli v Constantin Schmitz | 7-6,7-6 |
| ITF M15 Antalya | 2021/04/06 07:00 | Constantin Schmitz v Bogdan Bobrov | 6-1,6-4 |
| ITF M15 Antalya | 2021/03/30 08:30 | Pol Martin Tiffon v Constantin Schmitz | 6-4,7-6 |
| ITF M15 Oldenzaal | 2021/08/16 10:00 | Zachary Eisinga v Aloys J W Van Baal | 3-6,6-4,10-7 |
| ITF M15 Oldenzaal | 2021/08/15 07:30 | Zachary Eisinga v Flemming Peters | 6-0,6-3 |
| ITF M25 The Hague | 2021/06/27 08:00 | Dax Donders v Zachary Eisinga | 6-2,7-5 |
| ITF M25 Alkmaar | 2021/06/21 14:25 | Guillaume Dermiens v Zachary Eisinga | 4-6,7-5,13-11 |
| ITF M25 Alkmaar | 2021/06/20 12:30 | Lodewijk Weststrate v Zachary Eisinga | 2-6,1-6 |
| ITF M15 Cairo | 2021/05/04 08:00 | Zachary Eisinga v Martin Dimitrov | 1-6,6-7 |
| ITF M15 Cairo | 2021/05/03 08:00 | Zachary Eisinga v Ali Alshati | 3-6,6-0,10-8 |
| ITF M15 Cairo | 2021/04/28 10:00 | Zachary Eisinga v Shintaro Mochizuki | 4-6,2-6 |