2018 Estoril Open
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.
Singles main-draw entrants
Seeds
- Rankings are as of April 23, 2018.
Other entrants
The following players received wildcards into the singles main draw:
The following players received entry from the qualifying draw:
Withdrawals
- Before the tournament
David Ferrer → replaced by 
Cameron Norrie
Nick Kyrgios → replaced by 
Nicolás Kicker
Benoît Paire → replaced by 
Gastão Elias
Doubles main-draw entrants
Seeds
- Rankings are as of April 23, 2018.
Other entrants
The following pairs received wildcards into the doubles main draw:
Champions
Singles
- João Sousa def.
Frances Tiafoe, 6–4, 6–4
Doubles
- Kyle Edmund / Cameron Norrie def.
Wesley Koolhof / 
Artem Sitak, 6–4, 6–2