The pair left at 3 AM "holding hands," the witness goes on.
Meanwhile, back at The Box, Reed arrived with beau Paris Latsis.
"They were whispering into each other's ear and Paris kept leaning over the balcony to check out the fans below," a witness tells "Extra."
Kellan Lutz had an easier time getting into this party. The actor "rolled up with friends and some female models and seemed to be the most energetic of the crew. He was chatting and bopping to the music with Ashley Greene, who came with girlfriends."
"Gossip Girl" couple Ed Westwick and Jessica Szhor arrived around midnight, where they hung out with Ashley Greene.
"Jessica seemed exhausted and wasn't as into the party while Ed was walking around chatting with people and drinking champagne," the witness tells "Extra."
Fergie "made a low-key entrance around midnight after the Victoria's Secret fashion show, followed by [Black Eyed Peas band-mate] Taboo, and the two went to a VIP table that was blocked off by bodyguards," adds the insider.