A Justin Bieber impersonator landed in hot water over the weekend after he tricked the staff at a Las Vegas hotel into believing he was actually The Biebs — and ended up performing onstage in front of a packed crowd … TMZ has learned.

The bizarre incident went down Saturday night at the Wynn Las Vegas after DJ Gryffin was told Bieber was in town and wanted to crank out a surprise performance at XS Nightclub, according to sources with direct knowledge.

Our sources say Gryffin thought the Bieber imitator was the real deal and he even invited fake Justin into the booth before the impersonator hit the stage in the club to sing several of the hitmaker’s songs.