Stadium: Teremeer (4) Round: 26 Ground: Hardcourt outdoor
| ITF M15 Troisdorf | 2021/05/12 12:00 | Mertens, Yannick v Max Wiskandt | 7-6,6-3 |
| 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 Troisdorf | 2021/05/12 11:55 | Johnson, Luke v Walterscheid-Tukic, Nikolas | 1-6,6-4,6-4 |
| ITF M15 Troisdorf | 2021/05/11 08:00 | Johnson, Luke v Tanner, Gian Luca | 6-7,7-5,11-9 |
| ITF M15 Troisdorf | 2021/05/10 08:00 | Johnson, Luke v Caspar Schuetze | 6-2,6-2 |
| ITF M15 Troisdorf | 2021/05/09 08:00 | Johnson, Luke v Hermans, Mats | 6-1,6-4 |
| UK Pro League | 2021/05/02 14:00 | Johnson, Luke v Paris, Joshua | 2-6,3-6 |
| UK Pro League | 2021/05/01 10:15 | Daniel Cox v Johnson, Luke | 6-3,6-2 |
| UK Pro League | 2021/04/30 10:15 | Johnson, Luke v Nolan, William | 6-4,6-0 |
| UK Pro League | 2021/04/28 10:15 | Johnson, Luke v Paris, Joshua | 4-6,7-6,8-10 |