# 2021 Internazionali di Tennis Città di Trieste – Singles

Carlos Alcaraz was the defending champion but chose not to defend his title.
Tomás Martín Etcheverry won the title after defeating Thiago Agustín Tirante 6–1, 6–1 in the final.

## Seeds

* Damir Džumhur (semifinals)
* Antoine Hoang (second round)
* Tomás Martín Etcheverry (champion)
* Danilo Petrović (withdrew)
* Alessandro Giannessi (second round)
* Marco Trungelliti (first round, retired)
* Maximilian Marterer (semifinals)
* Thomas Fabbiano (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 | Final | Final | Final | Final |
| 1 | Damir Džumhur | 3 | 3 | | | | |
| Q | Thiago Agustín Tirante | 6 | 6 | | | | |
| Q | Thiago Agustín Tirante | 6 | 6 | Q | Thiago Agustín Tirante | 1 | 1 |
| | | | | 3 | Tomás Martín Etcheverry | 6 | 6 |
| 3 | Tomás Martín Etcheverry | 7 | 7 | 3 | Tomás Martín Etcheverry | 6 | 6 |
| Q | Timofey Skatov | 5 | 5 | | | | |

### 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 |
| 1 | D Džumhur | 6 | 7 | | | | | | | | | | | | | | |
| | A Collarini | 0 | 5 | | 1 | D Džumhur | 6 | 6 | | | | | | | | | |
| | P Krstin | 6 | 6 | | | P Krstin | 3 | 1 | | | | | | | | | |
| Q | V Durasovic | 3 | 2 | | | | | | | 1 | D Džumhur | 6 | 6 | | | | |
| | G Zeppieri | 3 | 6 | 6 | | | | | | 7 | M Marterer | 4 | 4 | | | | |
| Q | P Sakamoto | 6 | 3 | 3 | | G Zeppieri | 4 | 6 | 6$^4$ | | | | | | | | |
| WC | L Nardi | 3 | 4 | | 7 | M Marterer | 6 | 4 | 7$^7$ | | | | | | | | |
| 7 | M Marterer | 6 | 6 | | | | | | | | | | | 1 | D Džumhur | 3 | 3 |
| Q | TA Tirante | 6 | 6 | | | | | | | | | | | Q | TA Tirante | 6 | 6 |
| | A Pellegrino | 3 | 1 | | Q | TA Tirante | 6 | 6 | | | | | | | | | |
| | N Serdarušić | 3 | 3 | | | R Bonadio | 4 | 2 | | | | | | | | | |
| | R Bonadio | 6 | 6 | | | | | | | Q | TA Tirante | 7 | 6 | | | | |
| | D Ajduković | 7 | 3 | 3 | | | | | | LL | O Luz | 5 | 4 | | | | |
| PR | J Lenz | 5 | 6 | 6 | PR | J Lenz | 5 | 0 | | | | | | | | | |
| LL | O Luz | 4 | | | LL | O Luz | 7 | 6 | | | | | | | | | |
| 6 | M Trungelliti | 2$^r$ | | | | | | | | | | | | | | | |

### 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 | Semifinals |
| 5 | A Giannessi | 4 | 6 | 6 | | | | | | | | | | | | | | |
| | R Molleker | 6 | 2 | 1 | 5 | A Giannessi | 7$^{10}$ | 4 | 0 | | | | | | | | | |
| | GM Moroni | 2 | 6$^6$ | | | V Sachko | 6$^8$ | 6 | 6 | | | | | | | | | |
| | V Sachko | 6 | 7$^8$ | | | | | | | | V Sachko | 4 | 4 | | | | | |
| | A Arnaboldi | 6$^3$ | 1 | | | | | | | 3 | TM Etcheverry | 6 | 6 | | | | | |
| WC | R Haase | 7$^7$ | 6 | | WC | R Haase | 6 | 0 | 4 | | | | | | | | | |
| | C Ugo Carabelli | 3 | 5 | | 3 | TM Etcheverry | 4 | 6 | 6 | | | | | | | | | |
| 3 | TM Etcheverry | 6 | 7 | | | | | | | | | | | | 3 | TM Etcheverry | 7 | 7 |
| 8 | T Fabbiano | 3 | 4 | | | | | | | | | | | | Q | T Skatov | 5 | 5 |
| | L Giustino | 6 | 6 | | | L Giustino | 6 | 2 | 1 | | | | | | | | | |
| Q | T Skatov | 7 | 5 | 6 | Q | T Skatov | 1 | 6 | 6 | | | | | | | | | |
| | D Stricker | 5 | 7 | 4 | | | | | | Q | T Skatov | 6$^5$ | 6 | 7$^8$ | | | | |
| WC | F Cobolli | 7$^8$ | 6 | | | | | | | WC | F Cobolli | 7$^7$ | 1 | 6$^6$ | | | | |
| | M Vrbenský | 6$^6$ | 3 | | WC | F Cobolli | 6 | 6 | | | | | | | | | | |
| | F Meligeni Alves | 7$^7$ | 6$^3$ | 1 | 2 | A Hoang | 2 | 1 | | | | | | | | | | |
| 2 | A Hoang | 6$^5$ | 7$^7$ | 6 | | | | | | | | | | | | | | |