# 2021 Saint Petersburg Challenger II – Singles

Zizou Bergs was the defending champion but lost in the second round to Kacper Żuk.
Evgenii Tiurnev won the title after defeating Żuk 6–4, 6–2 in the final.

## Seeds

* Roman Safiullin (first round)
* Dmitry Popko (quarterfinals)
* Cem İlkel (first round)
* Marius Copil (semifinals)
* Rudolf Molleker (second round)
* Kacper Żuk (final)
* Christopher Eubanks (quarterfinals)
* Teymuraz Gabashvili (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 |
| WC | Evgenii Tiurnev | 7$^7$ | 6 | | | | |
| 4 | Marius Copil | 6$^4$ | 2 | | | | |
| 4 | Marius Copil | 6$^4$ | 2 | WC | Evgenii Tiurnev | 6 | 6 |
| | | | | 6 | Kacper Żuk | 4 | 2 |
| 6 | Kacper Żuk | 7$^9$ | 6 | 6 | Kacper Żuk | 4 | 2 |
| Q | Jiří Lehečka | 6$^7$ | 3 | | | | |

### 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 | R Safiullin | 4 | 6$^7$ | | | | | | | | | | | | | | |
| Q | M Bašić | 6 | 7$^9$ | | Q | M Bašić | 6 | 7$^7$ | | | | | | | | | |
| | R Ortega Olmedo | 6 | 6 | | | R Ortega Olmedo | 1 | 6$^3$ | | | | | | | | | |
| | R Quiroz | 3 | 3 | | | | | | | Q | M Bašić | 4 | 2 | | | | |
| | V Kopřiva | 4 | 2 | | | | | | | WC | E Tiurnev | 6 | 6 | | | | |
| WC | E Tiurnev | 6 | 6 | | WC | E Tiurnev | 6 | 2 | 6 | | | | | | | | |
| | A Çelikbilek | 6 | 6 | | | A Çelikbilek | 3 | 6 | 3 | | | | | | | | |
| 8 | T Gabashvili | 2 | 2 | | | | | | | | | | | WC | E Tiurnev | 7$^7$ | 6 |
| 4 | M Copil | 6 | 6 | | | | | | | | | | | 4 | M Copil | 6$^4$ | 2 |
| Alt | M Vrbenský | 3 | 1 | | 4 | M Copil | 5 | 6 | 6 | | | | | | | | |
| | D-h Lee | 6 | 1 | 1 | | A Vatutin | 7 | 3 | 1 | | | | | | | | |
| | A Vatutin | 0 | 6 | 6 | | | | | | 4 | M Copil | 7$^7$ | 7 | | | | |
| | D Ajduković | 7 | 6 | | | | | | | 7 | C Eubanks | 6$^1$ | 5 | | | | |
| | Shuichi Sekiguchi | 5 | 2 | | | D Ajduković | 3 | 3 | | | | | | | | | |
| Alt | J de Jong | 5 | 4 | | 7 | C Eubanks | 6 | 6 | | | | | | | | | |
| 7 | C Eubanks | 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 | Semifinals | Semifinals | Semifinals | Semifinals |
| 6 | K Żuk | 6 | 6 | | | | | | | | | | | | | | |
| | I Sijsling | 4 | 3 | | 6 | K Żuk | 1 | 6 | 6 | | | | | | | | |
| SE | Z Bergs | 6 | 6 | | SE | Z Bergs | 6 | 4 | 3 | | | | | | | | |
| | P Krstin | 2 | 1 | | | | | | | 6 | K Żuk | 6 | 6 | | | | |
| | P Kotov | 6 | 6 | | | | | | | | J Sock | 3 | 2 | | | | |
| Q | T van Rijthoven | 2 | 4 | | | P Kotov | 4 | 3 | | | | | | | | | |
| | J Sock | 5 | 6 | 6 | | J Sock | 6 | 6 | | | | | | | | | |
| 3 | C İlkel | 7 | 4 | 4 | | | | | | | | | | 6 | K Żuk | 7$^9$ | 6 |
| 5 | R Molleker | 6 | 7 | | | | | | | | | | | Q | J Lehečka | 6$^7$ | 3 |
| | E Karlovskiy | 3 | 5 | | 5 | R Molleker | 2 | 3 | | | | | | | | | |
| Q | J Lehečka | 6 | 7$^7$ | | Q | J Lehečka | 6 | 6 | | | | | | | | | |
| Q | M Pecotić | 2 | 6$^4$ | | | | | | | Q | J Lehečka | 6 | 6 | | | | |
| WC | D Yevseyev | 6 | 6 | | | | | | | 2 | D Popko | 4 | 4 | | | | |
| WC | V Uzakov | 0 | 0 | | WC | D Yevseyev | 4 | 6 | 4 | | | | | | | | |
| | N Serdarušić | 4 | 4 | | 2 | D Popko | 6 | 2 | 6 | | | | | | | | |
| 2 | D Popko | 6 | 6 | | | | | | | | | | | | | | |