2021 Open de Oeiras

Country	Player	Rank1	Seed
GER	Oscar Otte	154	1
FRA	Enzo Couacaud	185	2
IND	Ramkumar Ramanathan	195	3
USA	Ernesto Escobedo	205	4
ARG	Andrea Collarini	215	5
MAR	Elliot Benchetrit	240	6
ITA	Gian Marco Moroni	241	7
CZE	Zdeněk Kolář	246	8

• ¹ Rankings are as of 22 March 2021.^[1]

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

• Zdeněk Kolář def. Gastão Elias 6–4, 7–5.

• Mats Moraing / Oscar Otte def. Riccardo Bonadio / Denis Yevseyev 6–1, 6–4.