- Source: 2021 Open de Oeiras
The 2021 Open de Oeiras was a professional tennis tournament played on clay courts. It was the first edition of the tournament which was part of the 2021 ATP Challenger Tour. It took place in Oeiras, Portugal between 29 March and 3 April 2021.
Singles main-draw entrants
= Seeds
=1 Rankings are as of 22 March 2021.
= Other entrants
=The following players received wildcards into the singles main draw:
Nuno Borges
Tiago Cação
Gastão Elias
The following player received entry into the singles main draw as an alternate:
Harry Bourchier
The following players received entry from the qualifying draw:
Raúl Brancaccio
Evan Furness
Manuel Guinard
Denis Yevseyev
The following players received entry as lucky losers:
Francisco Cabral
Luís Faria
Champions
= Singles
=Zdeněk Kolář def. Gastão Elias 6–4, 7–5.
= Doubles
=Mats Moraing / Oscar Otte def. Riccardo Bonadio / Denis Yevseyev 6–1, 6–4.