The 300 star turned 41 in style on Saturday night (13Nov10) by hiring out The Darby restaurant in New York and inviting 100 guests to celebrate.
Adrien Brody, U2's Bono, actor Jason Statham and professional skateboarder Tony Hawk all turned out for the event, which saw Butler take the mic to sing Mustang Sally with Mayer.
Butler also gave a rendition of Oasis' Wonderwall, before Mayer sang his own hit Who Says, reports New York Post gossip column PageSix.
A source tells the publication, "He had a pretty good voice - it wasn't what you'd expect from the guy from 300. It was epic. He was also in the deejay booth a lot and got the deejay to play a lot of rock, '80s and funk."