| Singles | |
|---|---|
| 2021 Open de Oeiras III | |
| Champion |  Carlos Alcaraz |
| Runner-up |  Facundo Bagnis |
| Score | 6–4, 6–4 |
Pedro Cachin was the defending champion [1] but chose to not defend his title.
Carlos Alcaraz won the title after defeating Facundo Bagnis 6–4, 6–4 in the final.
Jiří Veselý (second round, retired)
Steve Johnson (first round) Federico Coria (second round) Pedro Martínez (second round)
Yannick Hanfmann (first round) Juan Ignacio Londero (first round) Facundo Bagnis (final)
Pedro Sousa (quarterfinals)| Semifinals | Final | ||||||||||||
 Taro Daniel | 2 | 7 | 2 | ||||||||||
| Carlos Alcaraz | 6 | 5 | 6 | ||||||||||
| Carlos Alcaraz | 6 | 6 | |||||||||||
| 7 | Facundo Bagnis | 4 | 4 | ||||||||||
| 7 | Facundo Bagnis | 6 | 6 | ||||||||||
 Hugo Gaston | 0 | 2 | |||||||||||
| First round | Second round | Quarterfinals | Semifinals | ||||||||||||||||||||||||
| 1 | J Veselý | 6 | 77 | ||||||||||||||||||||||||
| Q | H Grenier | 4 | 62 | 1 | J Veselý | 3 | 3r | ||||||||||||||||||||
 S Ofner | 1 | 64 |  H Dellien | 6 | 4 | ||||||||||||||||||||||
| H Dellien | 6 | 77 | H Dellien | 1 | 6 | 1 | |||||||||||||||||||||
 B Rola | 1 | 5 | T Daniel | 6 | 3 | 6 | |||||||||||||||||||||
| T Daniel | 6 | 7 | T Daniel | 6 | 6 | ||||||||||||||||||||||
| L Mayer | 4 | 6 | 6 | L Mayer | 3 | 4 | |||||||||||||||||||||
| 6 | JI Londero | 6 | 1 | 4 | T Daniel | 2 | 7 | 2 | |||||||||||||||||||
| 3 | F Coria | 2 | 6 | 6 | C Alcaraz | 6 | 5 | 6 | |||||||||||||||||||
| Q |  A Molčan | 6 | 4 | 1 | 3 | F Coria | 4 | 6 | 4 | ||||||||||||||||||
| M Cressy | 63 | 4 | WC | G Elias | 6 | 4 | 6 | ||||||||||||||||||||
| WC | G Elias | 77 | 6 | WC | G Elias | 5 | 4 | ||||||||||||||||||||
| C Alcaraz | 6 | 6 | C Alcaraz | 7 | 6 | ||||||||||||||||||||||
| Y Uchiyama | 0 | 3 | C Alcaraz | 3 | 6 | 6 | |||||||||||||||||||||
| B Nakashima | 6 | 6 | B Nakashima | 6 | 4 | 4 | |||||||||||||||||||||
| 5 | Y Hanfmann | 3 | 4 | ||||||||||||||||||||||||
| First round | Second round | Quarterfinals | Semifinals | ||||||||||||||||||||||||
| 7 | F Bagnis | 7 | 3 | ||||||||||||||||||||||||
| C Taberner | 5 | 2r | 7 | F Bagnis | 2 | 6 | 6 | ||||||||||||||||||||
 J Jung | 6 | 4 | 3 | Alt | F Ferreira Silva | 6 | 4 | 2 | |||||||||||||||||||
| Alt | F Ferreira Silva | 1 | 6 | 6 | 7 | F Bagnis | 6 | 5 | 7 | ||||||||||||||||||
| WC | N Borges | 6 | 6 | WC | N Borges | 1 | 7 | 5 | |||||||||||||||||||
| B Zapata Miralles | 4 | 4 | WC | N Borges | 6 | 6 | |||||||||||||||||||||
| WC | J Domingues | 4 | 2 | 4 | P Martínez | 2 | 4 | ||||||||||||||||||||
| 4 | P Martínez | 6 | 6 | 7 | F Bagnis | 6 | 6 | ||||||||||||||||||||
| 8 | P Sousa | 3 | 77 | 4 | H Gaston | 0 | 2 | ||||||||||||||||||||
 D Džumhur | 6 | 64 | 0r | 8 | P Sousa | 6 | 6 | ||||||||||||||||||||
| D Kudla | 4 | 6 | 5 |  B van de Zandschulp | 3 | 2 | |||||||||||||||||||||
| B van de Zandschulp | 6 | 3 | 7 | 8 | P Sousa | 3 | 6 | 2 | |||||||||||||||||||
| H Gaston | 77 | 6 | H Gaston | 6 | 1 | 6 | |||||||||||||||||||||
| Q |  Z Bergs | 61 | 1 | H Gaston | 6 | 6 | |||||||||||||||||||||
| Q |  E Gómez | 77 | 3 | 6 | Q | E Gómez | 4 | 3 | |||||||||||||||||||
| 2 | S Johnson | 64 | 6 | 3 | |||||||||||||||||||||||
David Ferrer was the defending champion, but lost in the quarterfinals to Dominic Thiem.
Pablo Cuevas was the defending champion and successfully defended his title, defeating Pablo Carreño Busta in the final, 7–6(7–4), 6–3.
Nicolás Kicker was the defending champion but was suspended from tennis due to match-fixing.
Guido Andreozzi was the defending champion but lost in the second round to Emilio Gómez.
This was the first edition of the tournament.
Fabio Fognini was the defending champion, but chose not to defend his title.
Guido Andreozzi was the defending champion but chose not to defend his title.
Tommy Robredo was the defending champion but retired in the first round against Maxime Janvier.
Juan Ignacio Londero was the defending champion, but lost to Laslo Đere in the quarterfinals.
Casper Ruud became the first Norwegian to win an ATP title, defeating Pedro Sousa in the final, 6–1, 6–4.
Salvatore Caruso was the defending champion and chose not to defend his title.
Carlos Alcaraz was the defending champion but chose not to defend his title.
Sander Arends and David Pel were the defending champions but chose not to defend their title.
Pedro Martínez defeated Sebastián Báez in the final, 4–6, 6–4, 6–4 to win the singles title at the 2022 Chile Open. It was his first ATP Tour title.
Francisco Cerúndolo defeated Sebastián Báez in the final, 7–6(7–4), 6–2 to win the men's singles tennis title at the 2022 Swedish Open. It was his maiden ATP Tour title.
Juan Pablo Varillas was the defending champion but lost in the first round to Thiago Agustín Tirante.
Zsombor Piros was the defending champion but chose not to defend his title.
Jaume Munar was the defending champion but lost in the quarterfinals to Alexandre Müller.
Pedro Cachin defeated Albert Ramos Viñolas in the final, 3–6, 6–0, 7–5 to win the singles tennis title at the 2023 Swiss Open Gstaad. It was his first ATP Tour singles title.
Sebastián Báez defeated Dominic Thiem in the final, 6–3, 6–1 to win the singles tennis title at the 2023 Austrian Open Kitzbühel. It was his third ATP Tour singles title. It was Thiem's first appearance in an ATP Tour final since the 2020 ATP Finals. Thiem was the second consecutive wildcard to reach the final, after Filip Misolic the previous year.