Stadium: Court 4 Round: 46 Ground: Grass
| Challenger Vancouver Qual | 2017/08/12 19:05 | Krajicek, Austin v Nielsen, Frederik | 2-6,3-6 |
| Challenger Busan Qual | 2017/05/14 03:10 | Krajicek, Austin v Nielsen, Frederik | 6-3,6-2 |
| Challenger Nottingham Qual | 2018/06/09 16:45 | Nielsen, Frederik v Zarichanskiy, D. | 6-3,6-1 |
| Challenger Loughborough | 2018/05/22 12:30 | Nielsen, Frederik v Guez, David | 2-6,4-6 |
| Challenger Loughborough Qual | 2018/05/21 09:30 | Haerteis, Johannes v Nielsen, Frederik | 6-7,1-6 |
| Challenger Loughborough Qual | 2018/05/20 09:30 | Carr, Simon v Nielsen, Frederik | 3-6,4-6 |
| Challenger Loughborough Qual | 2018/05/19 09:00 | Boutillier, Remi v Nielsen, Frederik | 7-6,6-7,1-6 |
| Challenger Busan Qual | 2018/05/14 03:30 | Yosuke Watanuki v Nielsen, Frederik | 1-6,6-4,6-0 |
| Challenger Busan Qual | 2018/05/13 04:10 | Nielsen, Frederik v Wishaya Trongcharoenchaikul | 6-7,6-4,6-0 |
| Challenger Seoul Qual | 2018/04/28 04:30 | Lim, Yong-Kyu v Nielsen, Frederik | 6-4,6-1 |
| Challenger Nottingham Qual | 2018/06/09 14:35 | Tiran Sanghera v Krajicek, Austin | 3-6,2-6 |
| Puerto Vallarta, Mexico | 2018/04/30 20:30 | Krajicek, Austin v Edan Leshem | 3-6,4-6 |
| Challenger - Mexique | 2018/04/10 21:20 | Londero, Juan Ignacio v Krajicek, Austin | 7-5,6-1 |
| Challenger Mexico City Qual | 2018/04/09 19:00 | Krajicek, Austin v Escobar, Gonzalo | 7-5,2-6,7-6 |
| Challenger Mexico City Qual | 2018/04/08 18:55 | Krajicek, Austin v Halebian, Alexios | 6-4,6-0 |
| Challenger Mexico City Qual | 2018/04/07 19:30 | Krajicek, Austin v Dzhanashia, Shalva | 6-3,6-3 |
| Challenger - San Luis Potosí | 2018/03/29 22:15 | Krajicek, Austin v Hernandez-Fernandez, Jose | 0-6,2-6 |
| Challenger - San Luis Potosí | 2018/03/29 01:10 | Lorenzi, Paolo v Krajicek, Austin | 7-6,1-6,3-6 |