# 2021 Sánchez-Casal Cup – Singles

Carlos Alcaraz was the defending champion but chose not to defend his title.
Dimitar Kuzmanov won the title after defeating Hugo Gaston 6–3, 6–0 in the final.

## Seeds

* Hugo Gaston (final)
* Alex Molčan (semifinals)
* Bernabé Zapata Miralles (first round, retired)
* Damir Džumhur (second round)
* Nikola Milojević (second round)
* Marc Polmans (first round)
* Cedrik-Marcel Stebe (withdrew)
* Jiří Lehečka (first round)

## 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 | Semifinals | Final | Final | Final | Final |
| 1 | Hugo Gaston | 6 | 0 | 6 | | | | |
| | Alexandre Müller | 2 | 6 | 0 | | | | |
| | Alexandre Müller | 2 | 6 | 0 | 1 | Hugo Gaston | 3 | 0 |
| | | | | | | Dimitar Kuzmanov | 6 | 6 |
| | Dimitar Kuzmanov | 7 | 7$^7$ | | | Dimitar Kuzmanov | 6 | 6 |
| 2 | Alex Molčan | 5 | 6$^5$ | | | | | |

### Top half

| First round | First round | First round | First round | First round | Second round | Second round | Second round | Second round | Quarterfinals | Quarterfinals | Quarterfinals | Quarterfinals | Semifinals | Semifinals | Semifinals | Semifinals | Semifinals |
| 1 | H Gaston | 7 | 6 | | | | | | | | | | | | | | |
| | A Collarini | 5 | 2 | | 1 | H Gaston | 6 | 6 | | | | | | | | | |
| LL | O Krutykh | 6 | 6 | | LL | O Krutykh | 0 | 2 | | | | | | | | | |
| WC | P Llamas Ruiz | 2 | 2 | | | | | | 1 | H Gaston | 6 | 6 | | | | | |
| | F Horanský | 6 | 2 | 7 | | | | | Q | N Álvarez Varona | 2 | 1 | | | | | |
| | M Marterer | 4 | 6 | 5 | | F Horanský | 4 | 3 | | | | | | | | | |
| Q | N Álvarez Varona | 6 | 7$^7$ | | Q | N Álvarez Varona | 6 | 6 | | | | | | | | | |
| 8 | J Lehečka | 2 | 6$^1$ | | | | | | | | | | 1 | H Gaston | 6 | 0 | 6 |
| 3 | B Zapata Miralles | 2 | 0$^r$ | | | | | | | | | | | A Müller | 2 | 6 | 0 |
| | J Barranco Cosano | 6 | 1 | | | J Barranco Cosano | 3 | 2 | | | | | | | | | |
| Alt | A Andreev | 4 | 1$^r$ | | | A Müller | 6 | 6 | | | | | | | | | |
| | A Müller | 6 | 4 | | | | | | | A Müller | 6 | 6 | | | | | |
| | D Popko | 6 | 6 | | | | | | Q | M Martineau | 3 | 2 | | | | | |
| | T Lamasine | 3 | 2 | | | D Popko | 6$^2$ | 2 | | | | | | | | | |
| Q | M Martineau | 6 | 6 | | Q | M Martineau | 7$^7$ | 6 | | | | | | | | | |
| 6 | M Polmans | 4 | 3 | | | | | | | | | | | | | | |

### Bottom half

| First round | First round | First round | First round | First round | Second round | Second round | Second round | Second round | Quarterfinals | Quarterfinals | Quarterfinals | Quarterfinals | Semifinals | Semifinals | Semifinals | Semifinals |
| LL | A López San Martín | 1 | 0 | | | | | | | | | | | | | |
| | N Borges | 6 | 6 | | | N Borges | 6$^6$ | 5 | | | | | | | | |
| WC | N Sánchez Izquierdo | 5 | 2 | | | T Gabashvili | 7$^8$ | 7 | | | | | | | | |
| | T Gabashvili | 7 | 6 | | | | | | | T Gabashvili | 2 | 0 | | | | |
| | D Kuzmanov | 6 | 6 | | | | | | | D Kuzmanov | 6 | 6 | | | | |
| | T Robredo | 0 | 1 | | | D Kuzmanov | 6 | 6 | | | | | | | | |
| Q | Georgii Kravchenko | 6 | 3 | 1 | 4 | D Džumhur | 4 | 4 | | | | | | | | |
| 4 | D Džumhur | 3 | 6 | 6 | | | | | | | | | | D Kuzmanov | 7 | 7$^7$ |
| 5 | N Milojević | 7 | 0 | 6 | | | | | | | | | 2 | A Molčan | 5 | 6$^5$ |
| Q | Y Oliel | 5 | 6 | 4 | 5 | N Milojević | 5 | 2 | | | | | | | | |
| | P Krstin | 4 | 4 | | | N Kuhn | 7 | 6 | | | | | | | | |
| | N Kuhn | 6 | 6 | | | | | | | N Kuhn | 3 | 2 | | | | |
| | M Guinard | 6 | 6$^4$ | 1 | | | | | 2 | A Molčan | 6 | 6 | | | | |
| | T Skatov | 3 | 7$^7$ | 6 | | T Skatov | 1 | 6$^6$ | | | | | | | | |
| WC | A Moro Cañas | 1 | 3 | | 2 | A Molčan | 6 | 7$^8$ | | | | | | | | |
| 2 | A Molčan | 6 | 6 | | | | | | | | | | | | | |