Ground: Clay
| ITF M25 Denia | 2025/07/23 09:30 | Sergi Perez Contri v Marcel Zielinski | 6-2,6-4 |
| ITF M15 Uslar | 2025/07/18 11:00 | Tadeas Paroulek v Marcel Zielinski | 6-3,7-5 |
| ITF M15 Uslar | 2025/07/17 14:23 | Marcel Zielinski v Nikolai Barsukov | 7-5,7-5 |
| ITF M15 Uslar | 2025/07/17 08:00 | Marcel Zielinski v Yannic Nittmann | 6-0,6-3 |
| ITF M15 Lodz | 2025/07/10 08:00 | Tarek Erlewein v Marcel Zielinski | 6-3,5-0 |
| ITF M15 Kamen | 2025/06/26 13:38 | Marcel Zielinski v Oscar Otte | 6-3,1-6,1-6 |
| ITF M15 Kamen | 2025/06/25 13:39 | Marcel Zielinski v Jannik Soetebier | 6-0,6-1 |
| ITF M15 Mungia-Laukariz | 2025/06/22 11:00 | Inaki Montes-De La Torre v Marcel Zielinski | 6-4,6-4 |
| ITF M15 Telfs | 2025/07/10 11:41 | Jonas P Hartenstein v Karl Friberg | 2-6,3-6 |
| ITF M15 Telfs | 2025/07/09 13:56 | Jonas P Hartenstein v Andrea De Marchi | 6-0,1-6,6-0 |
| ITF M15 Kamen | 2025/06/25 10:30 | Daniel Siniakov v Jonas P Hartenstein | 5-7,6-2,6-3 |
| ITF M15 Saarlouis | 2025/06/19 09:30 | Jonas P Hartenstein v Adrian Oetzbach | 1-6,3-6 |
| ITF M15 Saarlouis | 2025/06/18 11:30 | Jonas P Hartenstein v Nikolai Barsukov | 6-3,6-3 |
| ITF M15 Heraklion | 2025/04/02 10:29 | Jonas P Hartenstein v Alexis Canter | 2-6,7-6,6-7 |
| ITF M15 Heraklion | 2025/03/26 12:58 | Marcus Walters v Jonas P Hartenstein | 7-6,6-3 |
| ITF M25 Trimbach | 2025/03/05 15:17 | Jonas P Hartenstein v Mats Rosenkranz | 2-6,5-7 |