Jamie Foxx Sings 'Gold Digger' at Vegas Club Alongside Diplo

Jamie Foxx is ready to perform on the drop of a dime -- proven in his impromptu singing of one of his most famous songs ... which had an assist from Diplo.

The comedian hit XS Nightclub in Vegas Friday, rolling in around 3 AM with a large crew and joining Diplo -- who was DJ'ing -- onstage. Seems he was in the mood for a classic ... diving into his and Kanye's smash hit, "Gold Digger," as if it was 2005 all over again.

It's pretty cool to see Jamie belting out his old ditty ... dude hasn't lost a step, and people definitely haven't forgotten it either. They were singing along word for word. We're told Jamie stuck around a bit longer to help sing "Rack City."

JF wasn't the only celeb to pop in either ... Imagine Dragons' Dan Reynolds also made a cameo at XS. He showed up almost at 4 AM, and he too waved to the crowd from Diplo's elevated position. Dan also got on the mic a bit, but didn't sing or anything.

Speaking of Diplo ... he's on a bit of a high right now. The guy recently won a lawsuit against a woman who was allegedly harassing him, scoring a massive judgment in arbitration.