The 2018 Milex Open was a professional tennis tournament played on green clay courts. It was the fourth edition of the tournament which was part of the 2018 ATP Challenger Tour. It took place in Santo Domingo, Dominican Republic between 8 and 13 October 2018.
| Country | Player | Rank1 | Seed | |
|---|---|---|---|---|
| Pablo Cuevas | 66 | 1 | ||
 Argentina | Federico Delbonis | 91 | 2 | |
| Argentina | Guido Andreozzi | 99 | 3 | |
 Bolivia, Plurination;al State of | Hugo Dellien | 105 | 4 | |
 Italy | Paolo Lorenzi | 113 | 5 | |
 Brazil | Thiago Monteiro | 115 | 6 | |
| Argentina | Juan Ignacio Londero | 118 | 7 | |
| Argentina | Facundo Bagnis | 139 | 8 |
The following players received wildcards into the singles main draw:
The following players received entry into the singles main draw using protected rankings:
The following players received entry into the singles main draw as alternates:
The following players received entry from the qualifying draw:
See main article: 2018 Milex Open – Singles.
Federico Delbonis 6–4, 5–7, 6–4.See main article: 2018 Milex Open – Doubles.
Leander Paes / 
Miguel Ángel Reyes-Varela def. Ariel Behar / 
Roberto Quiroz 4–6, 6–3, [10–5].
