Round: 60 Ground: Hardcourt indoor
| ITF Croatia F2 | 2018/03/11 08:00 | Kai Lemstra v Marco De Rosa | 6-2,6-3 |
| ITF Croatia F1 | 2018/03/07 09:00 | Anze Arh v Kai Lemstra | 7-5,6-1 |
| ITF Germany F3 Qual | 2018/01/29 16:30 | Dominik Boehler v Kai Lemstra | 7-6,7-6 |
| ITF Germany F3 Qual | 2018/01/28 17:00 | Charley Emhardt v Kai Lemstra | 1-6,2-6 |
| ITF Germany F2 | 2018/01/23 15:35 | Kai Lemstra v Pedro Cachin | 3-6,3-6 |
| ITF Germany F1 | 2018/01/11 17:10 | Elmar Ejupovic v Kai Lemstra | 6-3,6-4 |
| ITF Germany F1 | 2018/01/10 11:45 | Stefan Seifert v Kai Lemstra | 6-2,6-7,4-6 |
| ITF Germany F1 | 2018/01/08 12:30 | Karlo Cubelic v Kai Lemstra | 6-4,2-6,4-6 |
| ITF Croatia F2 | 2018/03/12 11:00 | Valentin Royer v Philip Bachmaier | 6-2,6-4 |
| ITF Croatia F2 | 2018/03/11 08:00 | Michelangelo Endrizzi v Valentin Royer | 5-7,2-6 |