# 2021 Sibiu Open – Singles

Marc-Andrea Hüsler was the defending champion but lost in the semifinals to Thanasi Kokkinakis.
Stefano Travaglia won the title after defeating Kokkinakis 7–6$^{(7–4)}$, 6–2 in the final.

## Seeds

* Stefano Travaglia (champion)
* Radu Albot (first round)
* Alex Molčan (quarterfinals)
* Damir Džumhur (second round)
* Zdeněk Kolář (quarterfinals)
* Marc-Andrea Hüsler (semifinals)
* Thanasi Kokkinakis (final)
* Sumit Nagal (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 |
| 1 | Stefano Travaglia | 6 | 0 | 6 | | | | |
| 8 | Sumit Nagal | 4 | 6 | 0 | | | | |
| 8 | Sumit Nagal | 4 | 6 | 0 | 1 | Stefano Travaglia | 7$^7$ | 6 |
| | | | | | 7 | Thanasi Kokkinakis | 6$^4$ | 2 |
| 7 | Thanasi Kokkinakis | 6 | 6 | | 7 | Thanasi Kokkinakis | 6$^4$ | 2 |
| 6 | Marc-Andrea Hüsler | 2 | 1 | | | | | |

### Top half

| 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 | Semifinals |
| 1 | S Travaglia | 6 | 6 | | | | | | | | | | | | | | | |
| | L Rosol | 3 | 3 | 1 | S Travaglia | 6 | 6 | | | | | | | | | | | |
| Q | Yan Bondarevskiy | 6 | 6 | Q | Y Bondarevskiy | 3 | 2 | | | | | | | | | | | |
| WC | Vlad Andrei Dancu | 2 | 3 | | | | | | 1 | S Travaglia | 6 | 5 | 7$^8$ | | | | | |
| Q | Ștefan Paloși | 7 | 6 | | | | | | 5 | Z Kolář | 0 | 7 | 6$^6$ | | | | | |
| Q | ND Ionel | 5 | 1 | Q | Ș Paloși | 5 | 5 | | | | | | | | | | | |
| | M Copil | 5 | 4 | 5 | Z Kolář | 7 | 7 | | | | | | | | | | | |
| 5 | Z Kolář | 7 | 6 | | | | | | | | | | | 1 | S Travaglia | 6 | 0 | 6 |
| 4 | D Džumhur | 6 | 6 | | | | | | | | | | | 8 | S Nagal | 4 | 6 | 0 |
| WC | P Tsitsipas | 2 | 0 | 4 | D Džumhur | 2 | 6 | 2 | | | | | | | | | | |
| LL | Elmar Ejupovic | 1 | 3 | | G Blancaneaux | 6 | 4 | 6 | | | | | | | | | | |
| | G Blancaneaux | 6 | 6 | | | | | | | G Blancaneaux | 6$^3$ | 3 | | | | | | |
| | J Lehečka | 7$^7$ | 6 | | | | | | 8 | S Nagal | 7$^7$ | 6 | | | | | | |
| | FC Jianu | 6$^5$ | 2 | | J Lehečka | 5 | 3 | | | | | | | | | | | |
| | L Miedler | 3 | 1 | 8 | S Nagal | 7 | 6 | | | | | | | | | | | |
| 8 | S Nagal | 6 | 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 |
| 7 | T Kokkinakis | 6 | 6 | | | | | | | | | | | | | | |
| | M Marterer | 4 | 3 | | 7 | T Kokkinakis | 6 | 6 | | | | | | | | | |
| | E Kırkın | 7 | 4 | 6 | | E Kırkın | 1 | 1 | | | | | | | | | |
| | A Vatutin | 5 | 6 | 1 | | | | | | 7 | T Kokkinakis | 6 | 7$^7$ | | | | |
| | V Kopřiva | 7 | 7 | | | | | | | 3 | A Molčan | 2 | 6$^4$ | | | | |
| | D Petrović | 5 | 5 | | | V Kopřiva | 6 | 0 | 4 | | | | | | | | |
| | R Bonadio | 4 | 2 | | 3 | A Molčan | 1 | 6 | 6 | | | | | | | | |
| 3 | A Molčan | 6 | 6 | | | | | | | | | | | 7 | T Kokkinakis | 6 | 6 |
| 6 | M-A Hüsler | 6 | 6 | | | | | | | | | | | 6 | M-A Hüsler | 2 | 1 |
| | J Sels | 3 | 3 | | 6 | M-A Hüsler | 6 | 6 | | | | | | | | | |
| | J Clarke | 6$^5$ | 4 | | Q | Y Oliel | 4 | 1 | | | | | | | | | |
| Q | Y Oliel | 7$^7$ | 6 | | | | | | | 6 | M-A Hüsler | 7$^7$ | 6 | | | | |
| | F Agamenone | 6 | 7$^7$ | | | | | | | | F Agamenone | 6$^5$ | 4 | | | | |
| WC | VV Cornea | 1 | 6$^3$ | | | F Agamenone | 7$^7$ | 7 | | | | | | | | | |
| | V Sachko | 6 | 6 | | | V Sachko | 6$^4$ | 5 | | | | | | | | | |
| 2 | R Albot | 3 | 3 | | | | | | | | | | | | | | |