According to an eyewitness, Hayden Panettiere, 20, "was dancing, front and center" with Kevin Connolly, 35. The two were "chatting in the VIP lounge at the pool during the concert, and at the afterparty at LIV [nightclub at the Fontainebleau], they were sitting together. They were chatting all night, and they were very close to each other all evening."
The pair even shared a classic date food: Domino's New Pizza slices together poolside, says the eyewitness.
Lady Gaga performed four songs, including "Bad Romance" from her current album, Fame Monster. Others in the audience included Chace Crawford ("He was singing to Gaga's songs," says a source), blogger Perez Hilton (sporting a head-to-toe floral ensemble), former Desperate Housewives actor Shawn Pyfrom, The Hills' Frankie Delgado, former boybander J.C. Chasez and actress Stacy Keibler.
The AfterpartyAfter her set, Gaga "and over 20 of her dancers and production crew ate Domino's New Pizza. She spent over three hours backstage after the concert with her dancers. She thanked everyone individually for everything they had done in 2009," a source tells PEOPLE
The performer then headed to her 3,000-sq.-ft. penthouse where, a partygoer says, "the afterparty raged on until the wee hours of the morning."
As for the setting, the $35 million penthouse rents for $15,000 a night. "Lady Gaga has four bedrooms, a kitchen, whirlpool and amazing balcony overlooking the ocean," a source tells PEOPLE.
At the afterparty at LIV nightclub, in addition to Panettiere and Connolly, celebrating stars also included rappers Chris Brown, Bow Wow and Akon, who showed up via Diddy's private dinner party on the tony residential community of Star Island. A source says, "Chris was in great spirits, but once he was inside, he stuck to drinking bottled water. He pretty much kept to himself, hanging out with Akon."
With additional reporting by LINDA MARX