Usher was on the job Thursday night inside a crowded Los Angeles nightclub, giving a live performance at a vodka launch party, when two scuffling fans just about upstaged his concert.

Celebs in the stunned audience of 1,200 reportedly included Jenny McCarthy, Joe Jonas, Ryan Phillippe, Adam Lambert and 'DWTS' star Cheryl Burke.

And their shock probably had something to do with who was fighting: Oscar winner Jamie Foxx caused the commotion, according to RadarOnline, when an altercation with a former manager turned physical, midway through Usher's set.