Stadium: Teremeer (4) Round: 25 Ground: Hardcourt outdoor
| Sibenik, Singles M-ITF-CRO-05A | 2021/04/21 12:05 | Gergely Madarasz v Mertens, Yannick | 6-4,5-7,6-3 |
| ITF M25 Meerbusch | 2021/04/15 10:00 | Erler, Alexander v Mertens, Yannick | 6-3,3-6,6-1 |
| ITF M25 Meerbusch | 2021/04/13 13:30 | Mertens, Yannick v Vanneste, Jeroen | 6-3,6-4 |
| ITF - M15 Monastir | 2021/03/11 08:30 | Mertens, Yannick v Naoki Nakagawa | 6-4,3-6,4-6 |
| ITF - M15 Monastir | 2021/03/10 10:30 | Mertens, Yannick v Schmitz, Constantin | 6-0,6-2 |
| ITF - M15 Monastir | 2021/02/13 08:30 | Mertens, Yannick v Gauthier Onclin | 6-3,1-6,2-6 |
| ITF - M15 Monastir | 2021/02/12 10:05 | Mertens, Yannick v Juan Bautista Torres | 6-2,6-3 |
| ITF - M15 Monastir | 2021/02/11 08:25 | Mertens, Yannick v Mugevicius, Lukas | 6-1,6-1 |
| ITF M25 Meerbusch | 2021/04/11 14:00 | Voljacques, Hugo v Max Wiskandt | 4-6,6-1,10-0 |
| ITF - M15 Poitiers | 2021/03/18 09:30 | Breysach , Martin v Max Wiskandt | 6-2,6-7,6-4 |
| ITF - M15 Poitiers | 2021/03/17 09:00 | Oscar Moraing v Max Wiskandt | 3-6,7-6,0-6 |
| ITF - M15 Monastir | 2021/02/14 10:00 | Antonio Massara v Max Wiskandt | 6-4,6-4 |
| ITF - M15 Monastir | 2021/02/08 11:45 | Antonio Massara v Max Wiskandt | 7-6,3-6,10-6 |
| ITF - M15 Monastir | 2021/02/07 14:30 | Max Wiskandt v Taiyo Yamanaka | 2-6,7-5,11-9 |
| German Championship | 2020/12/09 12:00 | Timo Stodder v Max Wiskandt | 6-4,6-4 |
| German Championship | 2020/12/08 08:00 | Brinkmann, Nils v Max Wiskandt | 7-6,3-6,4-6 |