Round: 44 Ground: Carpet indoor
| ITF Germany F14 | 2018/09/30 11:30 | Marc Sieber v Patrick Nystroem | 6-1,7-5 |
| Challenger Sibiu Qual | 2018/09/16 12:00 | Nicolae Frunza v Marc Sieber | 6-4,6-3 |
| Challenger - Sevilia | 2018/09/01 16:00 | Marc Sieber v Bernabe Zapata Miralles | 6-7,3-6 |
| Challenger - Mallorca | 2018/08/26 11:30 | Federico Zeballos v Marc Sieber | 3-6,6-1,6-3 |
| Challenger - Meerbusch | 2018/08/14 12:30 | Marc Sieber v Johan Sebastien Tatlot | 6-7,6-4,4-6 |
| Challenger Meerbusch Qual | 2018/08/13 09:00 | Tristan Lamasine v Marc Sieber | 6-7,5-7 |
| Challenger Meerbusch Qual | 2018/08/12 09:40 | Marc Sieber v Adrian Oetzbach | 6-0,6-0 |
| Challenger Meerbusch Qual | 2018/08/11 11:45 | Mats Rosenkranz v Marc Sieber | 3-6,3-6 |
| ITF Switzerland F1 Qual | 2018/02/03 09:00 | Nicolas Parizzia v Henry V-D Schulenburg | 4-6,5-7 |