| Doubles | |
|---|---|
| 2021 Open de Oeiras IV | |
| Champions |  Jesper de Jong Tim van Rijthoven |
| Runners-up |  Julian Lenz  Roberto Quiroz |
| Score | 6–1, 7–6(7–3) |
Hunter Reese and Sem Verbeek were the defending champions [1] but chose not to defend their title.
Jesper de Jong and Tim van Rijthoven won the title after defeating Julian Lenz and Roberto Quiroz 6–1, 7–6(7–3) in the final.
Evan King / 
Gonçalo Oliveira (quarterfinals)
Sadio Doumbia / Fabien Reboul (first round) Dustin Brown / 
Tristan-Samuel Weissborn (quarterfinals)
Karol Drzewiecki / 
Sergio Martos Gornés (first round)| First round | Quarterfinals | Semifinals | Final | ||||||||||||||||||||||||
| 1 | E King G Oliveira | 5 | 78 | [10] | |||||||||||||||||||||||
R Ortega Olmedo  D Yevseyev | 7 | 66 | [7] | 1 | E King G Oliveira | 6 | 1 | [7] | |||||||||||||||||||
 P Cachin C Ugo Carabelli | 6 | 6 | P Cachin C Ugo Carabelli | 4 | 6 | [10] | |||||||||||||||||||||
 M Bortolotti  V Galović | 3 | 2 | P Cachin C Ugo Carabelli | 4 | 4 | ||||||||||||||||||||||
| 3 | D Brown T-S Weissborn | 6 | 6 | J de Jong T van Rijthoven | 6 | 6 | |||||||||||||||||||||
 S Galdós  F Zeballos | 4 | 1 | 3 | D Brown T-S Weissborn | 6 | 1 | [10] | ||||||||||||||||||||
| J de Jong T van Rijthoven | 6 | 6 | J de Jong T van Rijthoven | 4 | 6 | [12] | |||||||||||||||||||||
 C-h Tseng T-l Wu | 2 | 1 | J de Jong T van Rijthoven | 6 | 77 | ||||||||||||||||||||||
| R Bonadio N Serdarušić | 6 | 3 | [11] | J Lenz R Quiroz | 1 | 63 | |||||||||||||||||||||
| WC | Gonçalo Falcão Luís Faria | 3 | 6 | [9] | R Bonadio N Serdarušić | 2 | 2 | ||||||||||||||||||||
| WC | N Borges F Cabral | 77 | 66 | [11] | WC | N Borges F Cabral | 6 | 6 | |||||||||||||||||||
| 4 | K Drzewiecki S Martos Gornés | 64 | 78 | [9] | WC | N Borges F Cabral | 65 | 2 | |||||||||||||||||||
J Cerretani  VV Cornea | 6 | 4 | [4] | J Lenz R Quiroz | 77 | 6 | |||||||||||||||||||||
| WC | Pedro Araújo Fábio Coelho | 4 | 6 | [10] | WC | P Araújo F Coelho | 5 | 7 | [9] | ||||||||||||||||||
| J Lenz R Quiroz | 2 | 77 | [10] | J Lenz R Quiroz | 7 | 5 | [11] | ||||||||||||||||||||
| 2 | S Doumbia F Reboul | 6 | 65 | [3] | |||||||||||||||||||||||
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