Amy Adams -- CRUSHES Gay Bar Karaoke ... I've Got a 'Wicked' Voice

Amy Adams proved she can belt out showtunes with the best of 'em ... and by best of 'em, we mean the crowd at a gay karaoke bar in L.A. ... and TMZ has the footage.

Just days before winning the Golden Globe for Best Actress in a musical or comedy ... Adams hit up a gay bar and belted out a stellar rendition of "Defying Gravity" from "Wicked."

The performance may have been loud ... but we're told everyone in attendance was pretty impressed (and not just 'cause they were drunk.)