# 2021 Challenger de Santiago III – Singles

Juan Pablo Varillas was the defending champion but lost in the quarterfinals to Marcelo Tomás Barrios Vera.
Sebastián Báez won the title after defeating Felipe Meligeni Alves 3–6, 7–6$^{(8–6)}$, 6–1 in the final.

## Seeds

* Juan Manuel Cerúndolo (quarterfinals)
* Francisco Cerúndolo (quarterfinals)
* Juan Pablo Varillas (quarterfinals)
* Thiago Seyboth Wild (first round)
* Sebastián Báez (champion)
* Marcelo Tomás Barrios Vera (semifinals)
* Juan Ignacio Londero (second round)
* Enzo Couacaud (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 | Final |
| 5 | Sebastián Báez | 3 | 6 | 6 | | | | | |
| 6 | Marcelo Tomás Barrios Vera | 6 | 3 | 4 | | | | | |
| 6 | Marcelo Tomás Barrios Vera | 6 | 3 | 4 | 5 | Sebastián Báez | 3 | 7$^8$ | 6 |
| | | | | | | Felipe Meligeni Alves | 6 | 6$^6$ | 1 |
| | Felipe Meligeni Alves | 6 | 6 | | | Felipe Meligeni Alves | 6 | 6$^6$ | 1 |
| | Matheus Pucinelli de Almeida | 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 | Semifinals | Semifinals | Semifinals | Semifinals | Semifinals |
| 1 | JM Cerúndolo | 6 | 6 | | | | | | | | | | | | | | | |
| | J Lenz | 3 | 3 | | 1 | JM Cerúndolo | 6 | 3 | 6 | | | | | | | | | |
| WC | Benjamín Torres | 3 | 4 | | | P Cachin | 4 | 6 | 2 | | | | | | | | | |
| | P Cachin | 6 | 6 | | | | | | | 1 | JM Cerúndolo | 3 | 4 | | | | | |
| | JP Ficovich | 6 | 6 | | | | | | | 5 | S Báez | 6 | 6 | | | | | |
| | G Oliveira | 3 | 1 | | | JP Ficovich | 1 | 5 | | | | | | | | | | |
| Q | N Álvarez | 5 | 3 | | 5 | S Báez | 6 | 7 | | | | | | | | | | |
| 5 | S Báez | 7 | 6 | | | | | | | | | | | 5 | S Báez | 3 | 6 | 6 |
| 3 | JP Varillas | 6 | 6 | | | | | | | | | | | 6 | MT Barrios Vera | 6 | 3 | 4 |
| | F Mena | 4 | 2 | | 3 | JP Varillas | 6 | 1 | 6 | | | | | | | | | |
| | D Svrčina | 6 | 6 | | | D Svrčina | 4 | 6 | 4 | | | | | | | | | |
| Q | D Hidalgo | 2 | 0 | | | | | | | 3 | JP Varillas | 3 | 4 | | | | | |
| Q | R Matos | 2 | 6 | 4 | | | | | | 6 | MT Barrios Vera | 6 | 6 | | | | | |
| WC | D Fernández Flores | 6 | 4 | 6 | WC | D Fernández Flores | 0 | 1 | | | | | | | | | | |
| LL | L Catarina | 5 | 2 | | 6 | MT Barrios Vera | 6 | 6 | | | | | | | | | | |
| 6 | MT Barrios Vera | 7 | 6 | | | | | | | | | | | | | | | |

### Bottom 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 |
| 7 | JI Londero | 6 | 3 | 6 | | | | | | | | | | | | | |
| Alt | G Lama | 2 | 6 | 1 | 7 | JI Londero | 6 | 3 | 4 | | | | | | | | |
| Q | O Crawford | 6$^6$ | 3 | | | F Meligeni Alves | 2 | 6 | 6 | | | | | | | | |
| | F Meligeni Alves | 7$^8$ | 6 | | | | | | | | F Meligeni Alves | 6 | 5 | 7 | | | |
| | N Jarry | 6$^2$ | 4 | | | | | | | PR | G Melzer | 3 | 7 | 5 | | | |
| PR | G Melzer | 7$^7$ | 6 | | PR | G Melzer | 6 | 6 | | | | | | | | | |
| | TA Tirante | 6 | 4 | 6 | | TA Tirante | 2 | 0 | | | | | | | | | |
| 4 | T Seyboth Wild | 4 | 6 | 2 | | | | | | | | | | | F Meligeni Alves | 6 | 6 |
| 8 | E Couacaud | 1 | 1 | | | | | | | | | | | | M Pucinelli de Almeida | 2 | 4 |
| | M Pucinelli de Almeida | 6 | 6 | | | M Pucinelli de Almeida | 3 | 6 | 6 | | | | | | | | |
| | N Kicker | 6 | 6 | | | N Kicker | 6 | 2 | 4 | | | | | | | | |
| WC | M Soto | 3 | 0 | | | | | | | | M Pucinelli de Almeida | 7$^7$ | 2 | 6 | | | |
| Alt | N Chappell | 3 | 4 | | | | | | | 2 | F Cerúndolo | 6$^3$ | 6 | 4 | | | |
| Alt | H Casanova | 6 | 6 | | Alt | H Casanova | 2 | 5 | | | | | | | | | |
| Alt | F Díaz Acosta | 4 | 0 | | 2 | F Cerúndolo | 6 | 7 | | | | | | | | | |
| 2 | F Cerúndolo | 6 | 6 | | | | | | | | | | | | | | |