After a busy day – the singer's single "Roar" hit the Internet – Perry caught up with friends at the bar before heading upstairs to a private room for dinner.
"Katy and John were adorable," an onlooker tells PEOPLE. "Katy introduced him to people as her boyfriend and John affectionately held her close with his arm around her."
Just as the 15 guests were finishing their entrees, Perry's pal Rihanna arrived.
The "Diamonds" singer sat next to Perry and Mayer and the trio caught up. Rihanna even posted a snapshot with Perry on Instagram, writing "She. X She. #KatyAnna #RIHunited"
Having a much deserved cheers after a long day. I'm lifting my glass to ALL of you, couldn't have done it without you. CHEERS TO YOU #ROAR— Katy Perry (@katyperry) August 13, 2013