The duo celebrated at the "Hands to Myself" singer's afterparty at Light nightclub, where she was dressed in a blush silk Galvan dress with feathered Manolo Blahnik heels, reported Us magazine.
Gomez danced to Rihanna's "Work" with her girlfriends in their VIP booth while sipping on 50 Bleu cocktails.
"She was completely unfazed and continued to party when ex-boyfriend Justin Bieber's 'Sorry' came on," a source said.
Later in the evening, the songstress thanked the crowd for coming out and celebrating her first Vegas club appearance.