Stadium: Court M Round: 26 Ground: Clay
| Turkey F6, Singles Qualifying | 2017/02/18 08:00 | Heyman, Christopher v Sieber, Marc | 3-6,1-6 |
| Turkey F17, Singles Qualifying | 2016/05/01 11:00 | Sieber, Marc v Heyman, Christopher | 6-3,6-0 |
| Germany F8, Singles | 2018/07/17 14:05 | Viktor Durasovic v Sieber, Marc | 3-6,2-6 |
| Challenger Caltanissetta | 2018/06/12 08:00 | Arevalo-Gonzalez, Marcelo v Sieber, Marc | 1-6,6-1,7-5 |
| Challenger Caltanissetta Qual | 2018/06/11 10:15 | Souza, Joao Olavo v Sieber, Marc | 6-2,3-6,4-6 |
| Challenger Caltanissetta Qual | 2018/06/10 11:30 | Sieber, Marc v Pawel Juszczak | 6-0,6-1 |
| Challenger Caltanissetta Qual | 2018/06/09 13:25 | Balmashev, Mikhail v Sieber, Marc | 0-6,1-6 |
| Challenger Prostejov Qual | 2018/06/03 15:25 | Sieber, Marc v Satral, Jan | 6-4,3-6,4-6 |
| Challenger Prostejov Qual | 2018/06/03 09:45 | Nejedly, Pavel v Sieber, Marc | 1-6,5-7 |
| ITF Hungary F2 | 2018/05/18 08:00 | Mate Valkusz v Sieber, Marc | 6-1,6-1 |
| Germany F8, Singles | 2018/07/18 15:10 | Daljev, Pavle v Heyman, Christopher | 3-6,4-6 |
| ITF Belgium F3 | 2018/07/06 15:00 | Heyman, Christopher v Michael Geerts | 6-4,6-7,3-6 |
| ITF Belgium F3 | 2018/07/05 15:35 | Heyman, Christopher v Nikita Mashtakov | 6-3,6-2 |
| ITF Belgium F3 | 2018/07/04 10:10 | Heyman, Christopher v Martinez Sarrasague, Felipe | 6-2,6-4 |
| ITF Belgium F3 Qual | 2018/07/02 10:35 | Heyman, Christopher v Vanhauwe, Robin | 6-3,6-0 |
| ITF Belgium F3 Qual | 2018/07/01 12:00 | Heyman, Christopher v Lautaro Agustin Falabella | 6-2,6-1 |
| ITF Belgium F3 Qual | 2018/06/30 07:30 | Heyman, Christopher v Molina Bannen, Joaquin Pablo | 6-1,6-1 |
| ITF Germany F5 | 2018/06/28 13:30 | Heyman, Christopher v Tim Ruehl | 6-3,6-7,1-6 |