It hasn't been 2 months since Gerard Butler left rehab for substance abuse -- but last week, he was already back at an NYC bar, where he blew away the crowd with a knockout performance of "Wonderwall" ... and we got video!!!
Butler stopped by The Darby supper club in Manhattan last Thursday -- the actor didn't drink a drop ... but he did take the stage and perform several songs, including one by The Doors and another by The Rolling Stones.
But the best by far ... Butler's rendition of the Oasis classic "Wonderwall" -- you gotta check out the clip. After all.