"They were all hanging out in the VIP room," a source said. "They were all just talking and having a good time."
Don't worry, all was OK with Bieber, 18, and Gomez, 19, being in the 21-and-over club. The adults-only policy doesn't go into effect until the venue officially opens on Friday.
Also there were Perry's bestie, Raising Hope actress Shannon Woodward, former lovebirds Emma Roberts and Chord Overstreet, and Pretty Little Liars' Ashley Benson as well as club co-owners David Arquette and John Terzian.
Earlier in the evening Bieber and Gomez were at the premiere of Perry's new flick, Katy Perry: Part of Me 3D, at Grauman's Chinese Theatre. They then stopped by Chateau Marmont with R.Pattz, 26, before heading to Bootsy Bellows.
When they finally called it a night, Pattinson and Woodward almost had to hail a cab.
OK, maybe not. But bodyguards accidentally shut the doors on the celeb-filled van before they got in. They were quickly opened up when Woodward reminded them, "And there's still us."