Stadium: Court Kasro Round: 46
| Challenger Liberec Qual | 2018/07/28 08:00 | Juan Pablo Ficovich v Sieber, Marc | 3-6,6-3,3-6 |
| Challenger - Prague | 2018/07/24 11:30 | Nedovyesov, Aleksandr v Sieber, Marc | 6-0,6-4 |
| Challenger Prague Qual | 2018/07/23 10:10 | Torebko, Peter v Sieber, Marc | 1-6,4-6 |
| Challenger Prague Qual | 2018/07/22 14:10 | Dominik Kellovsky v Sieber, Marc | 3-6,6-7 |
| Challenger - Prague | 2018/07/21 14:05 | Perchicot, Mathieu v Sieber, Marc | 6-1,2-6,3-6 |
| Germany F8, Singles | 2018/07/19 09:30 | Sieber, Marc v Heyman, Christopher | 1-6,5-7 |
| 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 Liberec Qual | 2018/07/28 08:00 | Delic, Mate v Marvin Moeller | 3-6,1-6 |
| ATP Hamburg Qual | 2018/07/21 10:00 | Corentin Moutet v Marvin Moeller | 6-2,6-3 |
| Challenger Braunschweig Qual | 2018/07/07 14:30 | Dima, Dragos v Marvin Moeller | 7-6,6-1 |
| Challenger Braunschweig Qual | 2018/07/07 09:10 | Diarra, Gibril v Marvin Moeller | 5-7,5-7 |
| ITF Netherlands F1 | 2018/06/30 11:00 | Marvin Moeller v Botic Van De Zandschulp | 4-6,6-2,1-6 |
| ITF Netherlands F1 | 2018/06/29 12:00 | Marvin Moeller v Franco Emanuel Egea | 6-1,6-1 |
| ITF Netherlands F1 | 2018/06/28 13:55 | Marvin Moeller v Hermans, Mats | 6-2,6-2 |
| ITF Netherlands F1 | 2018/06/26 12:15 | Marvin Moeller v Pla Malfeito, Jaume | 6-1,3-6,6-4 |