Stadium: Court 2 Round: 25 Ground: Hardcourt outdoor
| Challenger Manama | 2021/11/22 08:00 | Haerteis, Johannes v Lazarov, Alexandar | 3-6,6-7 |
| Challenger Manama | 2021/11/21 10:05 | Haerteis, Johannes v Ammar Faleh Alhogbani | 6-2,6-1 |
| Helsinki, Finland | 2021/11/14 09:00 | Haerteis, Johannes v Viktor Durasovic | 4-6,6-7 |
| Challenger Eckental | 2021/11/02 18:15 | Maxime Cressy v Haerteis, Johannes | 6-7,6-4,6-3 |
| Challenger Eckental | 2021/11/01 11:15 | Haerteis, Johannes v Ignatik, Uladzimir | 4-6,6-2,7-6 |
| Challenger Eckental | 2021/10/31 13:30 | Lucas Miedler v Haerteis, Johannes | 3-6,7-5,3-6 |
| Challenger Ismaning | 2021/10/25 11:50 | Otto Virtanen v Haerteis, Johannes | 4-6,6-3,6-3 |
| Challenger Ismaning | 2021/10/24 12:35 | Haerteis, Johannes v Tristan Lamasine | 6-4,6-4 |
| Challenger Eckental | 2021/11/02 13:15 | Henri Squire v Erler, Alexander | 7-6,2-6,7-6 |
| Challenger Eckental | 2021/11/01 10:00 | Erler, Alexander v Henri Squire | 4-6,2-6 |
| Challenger Eckental | 2021/10/31 10:35 | Erler, Alexander v Dubrivnyy, Artem | 6-1,6-3 |
| ATP Vienna | 2021/10/23 09:00 | Erler, Alexander v Gianluca Mager | 7-6,2-6,4-6 |
| Challenger Bucharest | 2021/09/20 11:20 | Vitaliy Sachko v Erler, Alexander | 6-2,6-2 |
| Challenger Tulln | 2021/09/06 12:10 | Erler, Alexander v Lukas Rosol | 4-6,7-5,1-6 |
| Challenger Como | 2021/08/31 08:00 | Riccardo Bonadio v Erler, Alexander | 3-6,6-3,6-3 |
| Challenger Como | 2021/08/30 09:00 | Baldi, Filippo v Erler, Alexander | 6-7,4-6 |