Stadium: Pista 3 Round: 25 Ground: Hardcourt outdoor
| Challenger Mallorca | 2021/08/31 08:00 | Nicolas Moreno De Alboran v Johannes Haerteis | 3-6,6-4,4-6 |
| Challenger Mallorca | 2021/08/30 08:00 | Sergio Martos Gornes v Johannes Haerteis | 1-6,1-6 |
| Challenger - Praag | 2021/08/24 10:15 | Johannes Haerteis v Alex Rybakov | 4-6,2-6 |
| Challenger - Lüdenscheid | 2021/08/15 09:30 | Bogdan Bobrov v Johannes Haerteis | 1-6,6-4,6-3 |
| Challenger - Meerbusch | 2021/08/08 16:05 | Ivan Nedelko v Johannes Haerteis | 7-6,6-3 |
| Challenger - Segovia | 2021/07/27 13:05 | Altug Celikbilek v Johannes Haerteis | 6-3,6-4 |
| Challenger - Pozoblanco | 2021/07/20 20:10 | Cem Ilkel v Johannes Haerteis | 6-2,7-6 |
| Challenger - Amersfoort | 2021/07/13 08:30 | Mats Moraing v Johannes Haerteis | 6-1,6-0 |
| US Open | 2021/08/25 16:15 | Lukas Lacko v Holger Rune | 4-6,4-6 |
| ATP - Atlanta | 2021/07/24 19:25 | Jason Jung v Lukas Lacko | 6-4,6-7,6-3 |
| Challenger - Cary | 2021/07/19 23:45 | Mikael Torpegaard v Lukas Lacko | 6-4,6-2 |
| ATP - Newport | 2021/07/11 18:30 | Lukas Lacko v Brayden Schnur | 0-6,4-6 |
| Wimbledon | 2021/06/22 10:00 | Lukas Lacko v Nikola Milojevic | 4-6,4-6 |
| ATP - Halle | 2021/06/17 12:00 | Lloyd Harris v Lukas Lacko | 6-3,7-6 |
| ATP - Halle | 2021/06/15 09:00 | Guido Pella v Lukas Lacko | 7-6,5-7,1-6 |
| ATP - Halle | 2021/06/13 10:40 | Lukas Lacko v Joao Sousa | 4-6,6-4,6-3 |