# 2023 Open de Oeiras – Singles

Kaichi Uchida was the defending champion but lost in the quarterfinals to Juan Manuel Cerúndolo.
Zsombor Piros won the title after defeating Cerúndolo 6–3, 6–4 in the final.

## Seeds

* Adrian Mannarino (second round)
* Alexandre Müller (second round)
* Sebastian Ofner (semifinals)
* Juan Manuel Cerúndolo (final)
* João Sousa (first round)
* Kaichi Uchida (quarterfinals)
* Zsombor Piros (champion)
* Andrea Vavassori (quarterfinals)

## Draw
### Key

* Q = Qualifier
* WC = Wild card
* LL = Lucky loser
* Alt = Alternate
* SE = Special exempt
* PR = Protected ranking
* ITF = ITF entry
* JE = Junior exempt
* w/o = Walkover
* r = Retired
* d = Defaulted
* SR = Special ranking

### Finals

| Semifinals | Semifinals | Semifinals | Semifinals | Final | Final | Final | Final |
| 7/SE | Zsombor Piros | 6 | 6 | | | | |
| 3 | Sebastian Ofner | 4 | 2 | | | | |
| 3 | Sebastian Ofner | 4 | 2 | 7/SE | Zsombor Piros | 6 | 6 |
| | | | | 4 | Juan Manuel Cerúndolo | 3 | 4 |
| 4 | Juan Manuel Cerúndolo | 6 | 6 | 4 | Juan Manuel Cerúndolo | 3 | 4 |
| WC | Pedro Sousa | 2 | 4 | | | | |

### Top half

| First round | First round | First round | First round | First round | Second round | Second round | Second round | Second round | Second round | Quarterfinals | Quarterfinals | Quarterfinals | Quarterfinals | Quarterfinals | Semifinals | Semifinals | Semifinals | Semifinals |
| 1 | A Mannarino | 5 | 7 | 6 | | | | | | | | | | | | | | |
| | A Lazarov | 7 | 5 | 2 | 1 | A Mannarino | 6 | 2 | 3 | | | | | | | | | |
| | K Coppejans | 6 | 6 | | | K Coppejans | 4 | 6 | 6 | | | | | | | | | |
| Q | J Faria | 2 | 2 | | | | | | | | K Coppejans | 0 | 2 | | | | | |
| Q | D Mérida | 6 | 6 | | | | | | | 7/SE | Z Piros | 6 | 6 | | | | | |
| Q | C Crețu | 4 | 4 | | Q | D Mérida | 4 | 3 | | | | | | | | | | |
| | D Sweeny | 2 | 4 | | 7/SE | Z Piros | 6 | 6 | | | | | | | | | | |
| 7/SE | Z Piros | 6 | 6 | | | | | | | | | | | | 7/SE | Z Piros | 6 | 6 |
| 3 | S Ofner | 6 | 6 | | | | | | | | | | | | 3 | S Ofner | 4 | 2 |
| Q | P Nouza | 3 | 4 | | 3 | S Ofner | 2 | 6 | 6 | | | | | | | | | |
| | J McCabe | 2 | 6 | 7$^7$ | | J McCabe | 6 | 1 | 2 | | | | | | | | | |
| Alt | J Domingues | 6 | 3 | 6$^3$ | | | | | | 3 | S Ofner | 5 | 6 | 6 | | | | |
| | C-h Tseng | 6 | 6 | | | | | | | 8 | A Vavassori | 7 | 3 | 4 | | | | |
| LL | H Squire | 2 | 3 | | | C-h Tseng | 3 | 1 | | | | | | | | | | |
| | F Ferreira Silva | 2 | 0 | | 8 | A Vavassori | 6 | 6 | | | | | | | | | | |
| 8 | A Vavassori | 6 | 6 | | | | | | | | | | | | | | | |

### Bottom half

| First round | First round | First round | First round | Second round | Second round | Second round | Second round | Second round | Quarterfinals | Quarterfinals | Quarterfinals | Quarterfinals | Quarterfinals | Semifinals | Semifinals | Semifinals | Semifinals |
| 6 | K Uchida | 6 | 7$^7$ | | | | | | | | | | | | | | |
| | J De Loore | 4 | 6$^3$ | 6 | K Uchida | 6 | 1 | 6 | | | | | | | | | |
| | H Mayot | 3 | 4 | | A Andreev | 1 | 6 | 2 | | | | | | | | | |
| | A Andreev | 6 | 6 | | | | | | 6 | K Uchida | 3 | 3 | | | | | |
| | M Guinard | 1 | 0$^r$ | | | | | | 4 | JM Cerúndolo | 6 | 6 | | | | | |
| Q | P Llamas Ruiz | 6 | 3 | Q | P Llamas Ruiz | 4 | 3 | | | | | | | | | | |
| WC | D Vale | 4 | 4 | 4 | JM Cerúndolo | 6 | 6 | | | | | | | | | | |
| 4 | JM Cerúndolo | 6 | 6 | | | | | | | | | | | 4 | JM Cerúndolo | 6 | 6 |
| 5 | J Sousa | 1 | 3 | | | | | | | | | | | WC | P Sousa | 2 | 4 |
| | S Diez | 6 | 6 | | S Diez | 7$^7$ | 6 | | | | | | | | | | |
| | E Furness | 7 | 7$^7$ | | E Furness | 6$^2$ | 1 | | | | | | | | | | |
| Q | B Harris | 5 | 6$^3$ | | | | | | | S Diez | 5 | 6 | 3 | | | | |
| WC | P Sousa | 6 | 6 | | | | | | WC | P Sousa | 7 | 3 | 6 | | | | |
| WC | H Rocha | 3 | 4 | WC | P Sousa | 7 | 7$^7$ | | | | | | | | | | |
| | FC Jianu | 4 | 6$^3$ | 2 | A Müller | 5 | 6$^4$ | | | | | | | | | | |
| 2 | A Müller | 6 | 7$^7$ | | | | | | | | | | | | | | |