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.[1]
See main article: 2021 Estoril Open – Singles.
Albert Ramos Viñolas def. 
Cameron Norrie, 4–6, 6–3, 7–6(7–3).See main article: 2021 Estoril Open – Doubles.
Luke Bambridge / Dominic Inglot, 7–5, 3–6, [10–3].| Event | W | F | SF | QF | Round of 16 | Round of 32 | width=85 | Q | width=85 | Q2 | width=85 | Q1 |
| Singles | 250 | 150 | 90 | 45 | 20 | 0 | 12 | 6 | 0 | |||
|---|---|---|---|---|---|---|---|---|---|---|---|---|
| Doubles | 0 |
| Event | W | F | SF | QF | Round of 16 | Round of 32 | width=85 | Q2 | width=85 | 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 |
| Country | Player | Rank1 | Seed | |
|---|---|---|---|---|
 Canada | Denis Shapovalov | 14 | 1 | |
| Cristian Garín | 22 | 2 | ||
 France | Ugo Humbert | 31 | 3 | |
 Japan | ||||
 Kazakhstan | Alexander Bublik | 42 | 5 | |
| Marin Čilić | 44 | 6 | ||
| Spain | Albert Ramos Viñolas | 46 | 7 | |
| Spain | Alejandro Davidovich Fokina | 48 | 8 |
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:
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| Country | Player | Country | Player | Rank1 | Seed | |
|---|---|---|---|---|---|---|
| France | Fabrice Martin | France | Édouard Roger-Vasselin | 40 | 1 | |
| Raven Klaasen | Japan | Ben McLachlan | 67 | 2 | ||
| Austin Krajicek |  Austria | Oliver Marach | 70 | 3 | ||
| Marcelo Arévalo | Matwé Middelkoop | 93 | 4 |
The following pairs received wildcards into the doubles main draw:
Benoît Paire → replaced by 
Nicholas Monroe / Frances Tiafoe Marcel Granollers / Horacio Zeballos → replaced by Cristian Garín / David Vega Hernández]