Stadium: C Round: 45 Ground: Hardcourt outdoor
| ITF Spain F18 | 2016/06/21 17:30 | Nielsen, Frederik v Ortega-Olmedo, Roberto | 4-6,6-1,5-7 |
| Challenger Stockton | 2018/09/29 23:05 | Alexander Ritschard v Nielsen, Frederik | 6-4,7-6 |
| Challenger Tiburon | 2018/09/22 18:15 | Nielsen, Frederik v Sarkissian, Alexander | 4-6,5-7 |
| Challenger Cary | 2018/09/08 18:20 | Nielsen, Frederik v Song, Evan | 2-6,6-7 |
| Challenger Chicago | 2018/09/02 22:00 | Kaichi Uchida v Nielsen, Frederik | 6-3,6-4 |
| Challenger Chicago | 2018/09/02 15:00 | Joris De Loore v Nielsen, Frederik | 6-7,6-2,5-7 |
| Portoroz, Slovénie | 2018/08/07 08:00 | Lucas Miedler v Nielsen, Frederik | 6-3,6-2 |
| Challenger Portoroz Qual | 2018/08/06 08:00 | Nielsen, Frederik v Albano Olivetti | 6-2,7-6 |
| Challenger Portoroz Qual | 2018/08/05 08:00 | Andrea Pellegrino v Nielsen, Frederik | 0-6,0-6 |
| Challenger Stockton | 2018/09/29 17:00 | Ortega-Olmedo, Roberto v Marcos Giron | 4-6,4-6 |
| Challenger Tiburon | 2018/09/25 21:55 | Ernesto Escobedo v Ortega-Olmedo, Roberto | 6-1,7-6 |
| Challenger Tiburon | 2018/09/24 17:00 | Jan Choinski v Ortega-Olmedo, Roberto | 6-7,3-6 |
| Challenger Tiburon | 2018/09/23 17:00 | Marcos Giron v Ortega-Olmedo, Roberto | 3-6,6-1,5-7 |
| Challenger Tiburon | 2018/09/22 17:00 | Sebastian Fanselow v Ortega-Olmedo, Roberto | 1-6,2-6 |
| Challenger Columbus | 2018/09/17 16:35 | Alexei Popyrin v Ortega-Olmedo, Roberto | 4-6,7-6,7-5 |
| Challenger Cary | 2018/09/11 21:10 | Ortega-Olmedo, Roberto v Dominik Koepfer | 6-3,5-7,1-6 |
| Challenger Seville | 2018/09/03 08:30 | Alex Molcan v Ortega-Olmedo, Roberto | 7-5,6-3 |