The actress attended the opening of Light – where she took in acrobatic performances by Cirque du Soleil – with four pals early Saturday morning, an onlooker tells PEOPLE.
"The group was having a great time taking pictures, dancing, and taking tequila shots," the source says. "She looked amazing and they were all having a great time and just enjoying being out."
While the actress' boyfriend Dwyane Wade was busy playing with the Heat in Miami on Friday, Union, who is filming in Vegas, was enjoying hosting her pals for the weekend. "The girls she was with were her best friends and two of them came out to visit her," adds the source. "She was loving the time catching up with them."
Union took to Twitter early Saturday morning to write, "Oh Vegas ... I have missed you ..."
Memorial Day Weekend... Let the shenanigans begininstagram.com/p/ZtoADOJ-Z1/— Gabrielle Union (@itsgabrielleu) May 24, 2013
– Kevin O'Donnell