Stadium: Estadio Millennium Round: 29 Ground: Clay
| Challenger Alicante MD | 2018/04/02 12:35 | Koolhof/Sitak v Cervantes/Marrero | 6-4,6-1 |
| Challenger Irving MD | 2018/03/16 23:10 | Petzschner/Peya v Koolhof/Sitak | 6-4,7-5 |
| Challenger Irving MD | 2018/03/15 22:25 | Koolhof/Sitak v Krajicek/Lacko | 6-1,6-4 |
| Challenger Irving MD | 2018/03/14 19:00 | Inglot/Skupski v Koolhof/Sitak | 6-3,1-6,6-10 |
| ATP Sao Paulo MD | 2018/03/04 17:20 | Koolhof/Sitak v Delbonis/Gonzalez | 4-6,2-6 |
| ATP Sao Paulo MD | 2018/03/03 20:00 | Berlocq/Kicker v Koolhof/Sitak | 3-6,3-6 |
| ATP Sao Paulo MD | 2018/02/28 20:45 | Koolhof/Sitak v C Baena/Garcia-Lopez | 7-5,6-4 |
| ATP Sao Paulo MD | 2018/02/27 23:10 | Koolhof/Sitak v Arends/Begemann | 6-4,7-6 |