Federline and his entourage kicked off the evening with dinner at Tao at the Venetian, where Spears had dined with new pal Paris Hilton the previous weekend (and where Spears threw Federline a 28th birthday party back in March).
Before hitting the hotel and casino's club after dinner, Federline posed for photos in a dark pin-striped suit. He declined interviews but told photographers, "I'm good."
Once inside the club, Federline chilled at his VIP booth with about 15 friends, drinking Jack Daniels and sending text messages, but rarely chatting with the women at his table.
"He seemed really aware of his actions, but he was really having a good time," one clubgoer tells PEOPLE.
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As the night wore on, Federline and his crew danced when the DJ played his songs "Lose Control" and "Privilege." The group left after 4 a.m., headed for the Venetian's casino.