The 2018 Estoril Open (also known as the Millennium Estoril Open for sponsorship purposes) was a professional men's tennis tournament played on outdoor clay courts. It was the fourth edition of the Estoril Open, and part of the ATP World Tour 250 series of the 2018 ATP World Tour. The event took place at the Clube de Ténis do Estoril in Cascais, Portugal, from April 30 through May 6, 2018.
| Country | Player | Rank1 | Seed | |
|---|---|---|---|---|
| Kevin Anderson | 8 | 1 | ||
 Spain | Pablo Carreño Busta | 11 | 2 | |
 United Kingdom | Kyle Edmund | 23 | 3 | |
 Luxembourg | Gilles Müller | 28 | 4 | |
| Spain | Albert Ramos Viñolas | 40 | 5 | |
| Robin Haase | 44 | 6 | ||
 Argentina | Leonardo Mayer | 45 | 7 | |
 Russian Federation | Daniil Medvedev | 48 | 8 |
The following players received wildcards into the singles main draw:
The following players received entry from the qualifying draw:
David Ferrer → replaced by Cameron Norrie
Nick Kyrgios → replaced by Nicolás Kicker
Benoît Paire → replaced by Gastão Elias| Country | Player | Country | Player | Rank1 | Seed | |
|---|---|---|---|---|---|---|
| Australia | John Peers | Jean-Julien Rojer | 17 | 1 | ||
| Raven Klaasen |  New Zealand | Michael Venus | 48 | 2 | ||
| Spain | Marc López | Spain | David Marrero | 67 | 3 | |
 Brazil | Marcelo Demoliner |  Mexico | Santiago González | 84 | 4 |
The following pairs received wildcards into the doubles main draw:
See main article: 2018 Estoril Open – Singles.
Frances Tiafoe, 6–4, 6–4See main article: 2018 Estoril Open – Doubles.
Kyle Edmund / Cameron Norrie def. Wesley Koolhof / Artem Sitak, 6–4, 6–2