| Singles | |
|---|---|
| 2021 Open de Oeiras | |
| Champion |  Zdeněk Kolář |
| Runner-up |  Gastão Elias |
| Final score | 6–4, 7–5 |
This was the first of four editions of the tournament in the 2021 ATP Challenger Tour calendar. [1]
Zdeněk Kolář won the title after defeating Gastão Elias 6–4, 7–5 in the final.
Oscar Otte (first round)
Enzo Couacaud (first round)
Ramkumar Ramanathan (withdrew)
Ernesto Escobedo (first round)
Andrea Collarini (first round)
Elliot Benchetrit (first round)
Gian Marco Moroni (second round) Zdeněk Kolář (champion)| Semifinals | Final | ||||||||||||
| Marco Trungelliti | 3 | 2 | |||||||||||
| 8 | Zdeněk Kolář | 6 | 6 | ||||||||||
| 8 | Zdeněk Kolář | 6 | 7 | ||||||||||
| WC | Gastão Elias | 4 | 5 | ||||||||||
| WC | Gastão Elias | 6 | 7 | ||||||||||
| Q | Evan Furness | 3 | 5 | ||||||||||
| First round | Second round | Quarterfinals | Semifinals | ||||||||||||||||||||||||
| 1 | O Otte | 3 | 4 | ||||||||||||||||||||||||
| M Trungelliti | 6 | 6 | M Trungelliti | 6 | 6 | ||||||||||||||||||||||
| G Oliveira | 6 | 6 | G Oliveira | 1 | 3 | ||||||||||||||||||||||
| Q |  D Yevseyev | 1 | 2 | M Trungelliti | 6 | 6 | |||||||||||||||||||||
| Q | M Guinard | 1 | 5 |  I Sijsling | 3 | 4 | |||||||||||||||||||||
| I Sijsling | 6 | 7 | I Sijsling | 6 | 6 | ||||||||||||||||||||||
 A Vatutin | 4 | 3 | 7 | GM Moroni | 2 | 2 | |||||||||||||||||||||
| 7 | GM Moroni | 6 | 6 | M Trungelliti | 3 | 2 | |||||||||||||||||||||
| LL | F Cabral | 2 | 77 | 2 | 8 | Z Kolář | 6 | 6 | |||||||||||||||||||
| M Moraing | 6 | 65 | 6 | M Moraing | 6 | 2 | 5 | ||||||||||||||||||||
 D-h Lee | 3 | 4 | WC | T Cação | 4 | 6 | 7 | ||||||||||||||||||||
| WC | T Cação | 6 | 6 | WC | T Cação | 3 | 2 | ||||||||||||||||||||
| Alt |  H Bourchier | 5 | 4 | 8 | Z Kolář | 6 | 6 | ||||||||||||||||||||
 L Miedler | 7 | 6 | L Miedler | 1 | 1 | ||||||||||||||||||||||
| WC | N Borges | 6 | 66 | 1 | 8 | Z Kolář | 6 | 6 | |||||||||||||||||||
| 8 | Z Kolář | 2 | 78 | 6 | |||||||||||||||||||||||
| First round | Second round | Quarterfinals | Semifinals | ||||||||||||||||||||||||
| 5 | A Collarini | 6 | 3 | 5 | |||||||||||||||||||||||
 A Molčan | 3 | 6 | 7 | A Molčan | 6 | 6 | |||||||||||||||||||||
 N Serdarušić | 6 | 6 | N Serdarušić | 4 | 2 | ||||||||||||||||||||||
| LL | Luís Faria | 3 | 3 | A Molčan | 2 | 5 | |||||||||||||||||||||
 C-h Tseng | 3 | 6 | 4 | WC | G Elias | 6 | 7 | ||||||||||||||||||||
| WC | G Elias | 6 | 2 | 6 | WC | G Elias | 3 | 6 | 6 | ||||||||||||||||||
 R Ortega Olmedo | 7 | 6 | R Ortega Olmedo | 6 | 1 | 3 | |||||||||||||||||||||
| 4 | E Escobedo | 5 | 4 | WC | G Elias | 6 | 7 | ||||||||||||||||||||
| 6 | E Benchetrit | 3 | 1 | Q | E Furness | 3 | 5 | ||||||||||||||||||||
| Q | R Brancaccio | 6 | 6 | Q | R Brancaccio | 6 | 6 | ||||||||||||||||||||
| N Kuhn | 6 | 6 | N Kuhn | 1 | 2 | ||||||||||||||||||||||
| T Gabashvili | 3 | 3 | Q | R Brancaccio | 1 | 6 | 4 | ||||||||||||||||||||
 K Uchida | 6 | 4 | 63 | Q | E Furness | 6 | 1 | 6 | |||||||||||||||||||
| R Bonadio | 3 | 6 | 77 | R Bonadio | 6 | 3 | 4 | ||||||||||||||||||||
| Q | E Furness | 6 | 3 | 77 | Q | E Furness | 4 | 6 | 6 | ||||||||||||||||||
| 2 | E Couacaud | 4 | 6 | 64 | |||||||||||||||||||||||
Zdeněk Kolář is a Czech tennis player.
This was the first edition of the tournament as a Challenger event.
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