The 42-year-old actor reached the place with his two male friends, but later he was joined by the woman at a private table tucked in the back of the venue, reported E! online.
"They were attached at the hip and had their attention on one another all night," a source said.
"I'm not sure where his friends wandered off to, but this mystery brunette definitely had his full attention as Gerard stayed by her side the entire time he was at his table. They were flirting and dancing to the DJs," another source said.
Though enjoying his time at the club, Butler, who recently completed a rehab stint, stayed away from alcohol.
