After months of speculation about their relationship, he proudly accompanied his Stop-Loss costar Abbie Cornish to the 2008 Australian in Film Breakthrough Awards – their first major event as a couple.
"They were adorable," says a guest. "He had his arm around her and they were cozy and comfortable."
When Cornish – who was being honored with a Breakthrough Award – was introduced, Phillippe rubbed her back while she leaned against his shoulder. Throughout the evening, they held hands.
Phillippe, 33, also let Cornish enjoy her moment in the spotlight, waiting patiently as she worked the room and posed for photos. Once she was at his side once again, they continued to share laughs with pals.
The secret to Cornish's appeal? "We needed a girl who could knock back and drink the guys under the table, change a blown tire, whatever she needs to do," their Stop-Loss director, Kimberly Pierce, tells PEOPLE. "And she has that. She's that kind of girl."
A second Breakthrough Award went to actress Mia Wasikowska for her work in the HBO series In Treatment.
Phillippe and Cornish left the party just before 10 p.m., heading to Hennessy's weekly jazz night at Teddy's.