Stadium: Court 2 Round: 54 Ground: Clay
| Challenger Heilbronn Qual | 2018/05/13 09:00 | Hernan Casanova v Niesten, Miliaan | 1-6,5-7 |
| Challenger Heilbronn Qual | 2018/05/12 09:00 | Niesten, Miliaan v Mathieu Meyer | 6-1,6-3 |
| ITF Spain F10 | 2018/04/24 08:00 | Niesten, Miliaan v Romero de Avila Senise, Alberto | 3-6,2-6 |
| ITF Portugal F8 | 2018/04/21 14:10 | Niesten, Miliaan v Cacao, Tiago | 4-6,5-7 |
| ITF Portugal F8 | 2018/04/20 10:00 | Niesten, Miliaan v Barry, Sam | 6-3,6-4 |
| ITF Portugal F8 | 2018/04/18 12:10 | Sao Thiago, Igor v Niesten, Miliaan | 1-6,3-6 |
| ITF Portugal F7 | 2018/04/12 12:20 | Niesten, Miliaan v Frederico Ferreira Silva | 0-6,5-7 |
| ITF Portugal F7 | 2018/04/11 09:00 | Prechtel, Sebastian v Niesten, Miliaan | 6-7,2-6 |
| Challenger Heilbronn Qual | 2018/05/13 09:00 | Christoph Negritu v Igor Sijsling | 4-6,0-6 |
| Challenger - Glasgow | 2018/05/03 09:30 | Igor Sijsling v Ortega-Olmedo, Roberto | 6-1,6-7,6-7 |
| Challenger - Glasgow | 2018/05/01 09:30 | Bernabe Zapata Miralles v Igor Sijsling | 1-6,3-6 |
| ITF Portugal F8 | 2018/04/17 10:00 | Gigounon, Germain v Igor Sijsling | 6-4,6-2 |
| ITF Portugal F7 | 2018/04/12 17:40 | Gigounon, Germain v Igor Sijsling | 6-4,6-3 |
| ITF Portugal F7 | 2018/04/12 11:00 | Igor Sijsling v Monteiro, Joao | 6-2,6-1 |
| Challenger St Brieuc Qual | 2018/03/26 11:05 | Constant Lestienne v Igor Sijsling | 6-2,5-7,7-6 |
| Challenger St Brieuc Qual | 2018/03/25 11:55 | Igor Sijsling v Zizou Bergs | 7-5,7-5 |