Hadjar took the second victory of his F2 career with a dominant drive at Albert Park as he skilfully navigated two safety car restarts to win by over six seconds.
But the result carries a significant asterisk, with the stewards set to investigate a start-line incident that resulted in Pepe Marti and Gabriel Bortoleto retiring after only travelling a matter of metres.
Unaware of the fast-starting Marti to his right, Hadjar veered across the track and caused contact between the Campos driver and second-placed starter Bortoleto, with the pair making heavy contact with the wall.
For Marti, this was his second opening-lap retirement in succession following a collision in the Saudi Arabian feature race. This latest incident will be investigated after the race.
Having beaten polesitter Roman Staněk into Turn 1, Hadjar headed the field during the five-lap safety car period to allow for the clear-up operation.
Other early movers included championship leader Zane Maloney, who progressed from sixth to fourth as a result of the two retirements ahead, while Victor Martins - who caused a red flag in qualifying and failed to set a time - leapt from 21st to 13th.
Source: Autosport