Greg Hardy made one hell of an impression on Dana White -- knocking out his opponent 57 seconds into his UFC Contender Series fight.
Hardy was matched up against another former NFL lineman Austen Lane Tuesday night -- and the winner gets an opportunity to earn a UFC contract ... if White feels like the fighter has earned it.
Hardy -- who was undefeated in his previous 3 amateur MMA fights -- hit the Octagon like a violent tornado ... and rocked Lane -- who was 2-0 with 2 KOs in his previous pro fights -- with a couple of devastating haymakers.
Lane went down ... and the ref called it immediately for Hardy.
Dana White has previously told TMZ Sports he feels Hardy deserves a second chance -- the question now is ... will he get a UFC contract as part of it?