Keith Urban provided backing vocals.
Turning 40 never looked so fun.
Read: Bruce Springsteen Signs Young Fan's School Tardy Note After Late Concert
Reese Witherspoon took the stage to sing “Sweet Home Alabama” with Keith Urban backing her up during her birthday bash on Saturday night.
Taylor Swift also performed at the Oscar winner’s star-studded bash inside L.A. venue Warwick.
Other celebs in attendance included Kate Hudson, Isla Fisher, Chelsea Handler, Courteney Cox, Jennifer Aniston and husband Justin Theroux.
Read: Ben Affleck Says His Son Thinks He Really Is Batman At 'Batman V. Superman' Premiere
Earlier, the birthday girl took a funny video with her mom as they got pumped up to party.
Watch: Dad Defends Spending $6 Million On His Daughter's Quinceanera
