| 2021 Sibiu Open | |
|---|---|
| Date | 27 September – 3 October |
| Edition | 10th |
| Location | Sibiu, Romania |
| Champions | |
| Singles | |
 Stefano Travaglia | |
| Doubles | |
 Alexander Erler / Lucas Miedler | |
The 2021 Sibiu Open was a professional tennis tournament played on clay courts. It was the tenth edition of the tournament which was part of the 2021 ATP Challenger Tour. It took place in Sibiu, Romania between 27 September and 3 October 2021.
| Country | Player | Rank1 | Seed |
|---|---|---|---|
| ITA | Stefano Travaglia | 98 | 1 |
 MDA | Radu Albot | 104 | 2 |
 SVK | Alex Molčan | 118 | 3 |
 BIH | Damir Džumhur | 129 | 4 |
 CZE | Zdeněk Kolář | 149 | 5 |
 SUI | Marc-Andrea Hüsler | 159 | 6 |
 AUS | Thanasi Kokkinakis | 183 | 7 |
 IND | Sumit Nagal | 185 | 8 |
The following players received wildcards into the singles main draw:
Victor Vlad Cornea Vlad Andrei Dancu
Petros Tsitsipas The following players received entry from the qualifying draw:
Yan Bondarevskiy David Ionel 
Yshai Oliel Ștefan PaloșiThe following player received entry as a lucky loser:
Elmar Ejupovic Stefano Travaglia def. Thanasi Kokkinakis 7–6(7–4), 6–2. Alexander Erler / Lucas Miedler def. 
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