After performing at L.A.'s Staples Center with guest Eminem
had beau Matt Kemp
by her side for a late-night bash at Drai's in the W Hollywood. Arriving after 1 a.m., the pop star was delivered a cake with sparklers. She also shared some smooches with Kemp, and listened as rapper Lil Jon
performed his hits for the crowd. Also there: Brody Jenner
and Avril Lavigne
, who hung out in the outside, back bar with friends.