2021 Estoril Open
The 2021 Estoril Open is a men's tennis tournament played on outdoor clay courts. It is the 6th edition of the tournament and part of the ATP Tour 250 series of the 2021 ATP Tour. It tames place at the Clube de Ténis do Estoril in Cascais, Portugal, from 26 April through 2 May 2021. Seventh-seeded Albert Ramos Viñolas won the singles title.
Champions
Singles
Albert Ramos Viñolas def. Cameron Norrie, 4–6, 6–3, 7–6.Doubles
Hugo Nys / Tim Pütz def. Luke Bambridge / Dominic Inglot, 7–5, 3–6, .Points and prize money
Prize money
| Event | W | F | SF | QF | Round of 16 | Round of 32 | Q2 | Q1 |
| Singles | €41,145 | €29,500 | €21,000 | €14,000 | €9,000 | €5,415 | €2,645 | €1,375 |
| Doubles* | €15,360 | €11,000 | €7,250 | €4,710 | €2,760 |
*per team
Singles main-draw entrants
Seeds
Other entrants
The following players received wildcards into the main draw:The following players received entry from the qualifying draw:
The following player received entry as a lucky loser:
Withdrawals
;Before the tournament- Pablo Carreño Busta → replaced by Kevin Anderson
- Fabio Fognini → replaced by Pierre-Hugues Herbert
- Gaël Monfils → replaced by Marco Cecchinato
- Kei Nishikori → replaced by Roberto Carballés Baena
- Benoît Paire → replaced by Fernando Verdasco
- Diego Schwartzman → replaced by Juan Ignacio Londero
Retirements
Doubles main-draw entrants
Seeds
- Rankings are as of 19 April 2021
Other entrants
The following pairs received wildcards into the doubles main draw:Withdrawals
;Before the tournament- Romain Arneodo / Benoît Paire → replaced by Nicholas Monroe / Frances Tiafoe
- Marcel Granollers / Horacio Zeballos → replaced by Cristian Garín / David Vega Hernández