# 2021 Biella Challenger Indoor II – Singles

This was the second of seven editions of the tournament in the 2021 tennis season. Illya Marchenko was the defending champion but lost in the quarterfinals to Andreas Seppi.
Kwon Soon-woo won the title after defeating Lorenzo Musetti 6–2, 6–3 in the final.

## Seeds

* Alejandro Davidovich Fokina (second round)
* Sebastian Korda (first round)
* Kwon Soon-woo (champion)
* Andreas Seppi (semifinals)
* Kamil Majchrzak (second round)
* Antoine Hoang (first round)
* Lorenzo Musetti (final)
* Evgeny Donskoy (semifinals)

## 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 |
| 8 | Evgeny Donskoy | 3 | 7$^7$ | 1 | | | | |
| 3 | Kwon Soon-woo | 6 | 6$^4$ | 6 | | | | |
| 3 | Kwon Soon-woo | 6 | 6$^4$ | 6 | 3 | Kwon Soon-woo | 6 | 6 |
| | | | | | 7 | Lorenzo Musetti | 2 | 3 |
| 4 | Andreas Seppi | 6 | 3 | 4 | 7 | Lorenzo Musetti | 2 | 3 |
| 7 | Lorenzo Musetti | 3 | 6 | 6 | | | | |

### 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 | A Davidovich Fokina | 6 | 6 | | | | | | | | | | | | | | |
| | S Diez | 3 | 0 | | 1 | A Davidovich Fokina | 6$^2$ | 4 | | | | | | | | | |
| | F Gaio | 6 | 6 | | | F Gaio | 7$^7$ | 6 | | | | | | | | | |
| LL | H Moriya | 3 | 1 | | | | | | | F Gaio | 3 | 2 | | | | | |
| Q | C Lestienne | 5 | 7$^{12}$ | 7$^7$ | | | | | 8 | E Donskoy | 6 | 6 | | | | | |
| WC | L Nardi | 7 | 6$^{10}$ | 6$^0$ | Q | C Lestienne | 4 | 2 | | | | | | | | | |
| | M Safwat | 3 | 4 | | 8 | E Donskoy | 6 | 6 | | | | | | | | | |
| 8 | E Donskoy | 6 | 6 | | | | | | | | | | 8 | E Donskoy | 3 | 7$^7$ | 1 |
| 3 | S-w Kwon | 6 | 6 | | | | | | | | | | 3 | S-w Kwon | 6 | 6$^4$ | 6 |
| | J Jung | 3 | 4 | | 3 | S-w Kwon | 6 | 6 | | | | | | | | | |
| | R Marcora | 7$^7$ | 6 | | | R Marcora | 2 | 2 | | | | | | | | | |
| | H Laaksonen | 6$^4$ | 1 | | | | | | 3 | S-w Kwon | 6 | 6 | | | | | |
| | A Giannessi | 1 | 4 | | | | | | | Y Maden | 2 | 1 | | | | | |
| | T Fabbiano | 6 | 6 | | | T Fabbiano | 6$^3$ | 1 | | | | | | | | | |
| | Y Maden | 6 | 6 | | | Y Maden | 7$^7$ | 6 | | | | | | | | | |
| 6 | A Hoang | 0 | 2 | | | | | | | | | | | | | | |

### 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 | Semifinals | Semifinals | Semifinals | Semifinals | Semifinals |
| 5 | K Majchrzak | 7$^7$ | 6 | | | | | | | | | | | | | | | |
| | B Rola | 6$^5$ | 4 | | 5 | K Majchrzak | 6 | 4 | 1 | | | | | | | | | |
| SE | I Marchenko | 7$^7$ | 4 | 6 | SE | I Marchenko | 1 | 6 | 6 | | | | | | | | | |
| WC | G Zeppieri | 6$^1$ | 6 | 3 | | | | | | SE | I Marchenko | 4 | 5 | | | | | |
| | B Zapata Miralles | 6$^5$ | 4 | | | | | | | 4 | A Seppi | 6 | 7 | | | | | |
| | M Kližan | 7$^7$ | 6 | | | M Kližan | 6$^8$ | 3 | | | | | | | | | | |
| Q | M Viola | 2 | 6 | 5 | 4 | A Seppi | 7$^{10}$ | 6 | | | | | | | | | | |
| 4 | A Seppi | 6 | 4 | 7 | | | | | | | | | | 4 | A Seppi | 6 | 3 | 4 |
| 7 | L Musetti | 7 | 6 | | | | | | | | | | | 7 | L Musetti | 3 | 6 | 6 |
| WC | S Napolitano | 5 | 3 | | 7 | L Musetti | 6 | 6 | | | | | | | | | | |
| Q | B Kavčič | 3 | 2 | | Alt | L Lacko | 4 | 3 | | | | | | | | | | |
| Alt | L Lacko | 6 | 6 | | | | | | | 7 | L Musetti | 6 | 6 | | | | | |
| Q | R Brancaccio | 6 | 3 | 4 | | | | | | Alt | E Gulbis | 2 | 4 | | | | | |
| Alt | E Gulbis | 4 | 6 | 6 | Alt | E Gulbis | 6 | 6 | | | | | | | | | | |
| | D Popko | 6 | 6 | | | D Popko | 1 | 4 | | | | | | | | | | |
| 2 | S Korda | 4 | 3 | | | | | | | | | | | | | | | |