KIIS-FM's annual Wango Tango festival stormed Los Angeles' Staples Center on Saturday night. While the energy was massive inside the sold-out arena -- with a bill that included [artist id="1270"]Usher[/artist], [artist id="3187077"]Justin Bieber[/artist], [artist id="961097"]Ludacris[/artist], [artist id="3213641"]Ke$ha[/artist], [artist id="1240040"]Akon[/artist], [artist id="3188063"]Adam Lambert[/artist] and [artist id="1243216"]David Guetta[/artist] -- it was equally buzzing backstage with artists and entourages mixing it up.

Maybe they enjoyed themselves a little too much, as Ke$ha joked that she had already made out with glam-man Adam Lambert by the time she made it to our interview. She was also looking forward to corrupting pint-sized popster Bieber. No doubt she was excited to take part in the show, which has become an institution in the music industry and a signal that artists have made it.

"I'm gonna treat it like a big fun summer dance party," Ke$ha told MTV News. "But I have to say, it's an honor [to perform] and I'm a little nervous."

Sharing that excitement was Wango Tango veteran Ludacris, who shouted, "Three-peat! Three-peat!" He continued, "This is my third time doing it, so it feels good to have done it that many times."

While the artists were amped to participate, KIIS-FM DJ and multitasker Ryan Seacrest shared what was really setting the vibe backstage.

"The vibe is 'Where is Justin Bieber?' -- that's the vibe,"

Seacrest said. "All the girls that are hanging out here, even the ones that work for us, are like, 'Have you seen him?' I'm like, 'I'm right here.' They're like, 'No, no. Justin Bieber him.' "

When Bieber took the stage later in the night, he sent the Staples Center into an uproar. He was welcomed onstage by some people who know a thing or two about screaming crowds: Ashley Greene, Nikki Reed and other cast members of the upcoming "Twilight" film "Eclipse."

The 16-year-old Canadian sensation started his seven-song set with "Love Me," an ode to the '90s greatness of the Cardigans' "Lovefool."

Bieber, wearing a gray military jacket and a set of dog tags around his neck, followed with "One Less Lonely Girl." To the envy of every teen girl in the crowd, Justin serenaded a lucky female fan onstage and handed her a bouquet of flowers, giving her a big hug at the end.

Next up in Bieber's arsenal were "Somebody to Love," "U Smile" and "One Time." Then, in one of the most impressive performances of the night, Bieber sang and danced along to Michael Jackson's classic "Wanna Be Startin' Somethin' " while his dancers took turns doing freestyle dance moves. Backed by a live band, the medley then shifted into Aerosmith's "Walk This Way." Bieber proclaimed, "Put your rock stars in the air!" and the crowd raised their hands up in the famous devil horns gesture.

During the cover, bandmembers took turns doing solos, ending with Justin on the drums playing a solo of his own. If the crowd hadn't gotten enough, Justin closed his set with "Baby," the biggest sing-along of the night.

Ludacris quickly followed Bieber with a slew of hits, including "Stand Up," "What's Your Fantasy" and "My Chick Bad." British singer Taio Cruz joined Luda onstage for their current hit "Break Your Heart."

From one Atlanta artist to another, Usher followed up Luda's set with a nearly hour-long performance that spanned his entire catalogue. Usher worked hard all night, dancing and sweating through his set. Most impressive, though, was his voice, which wasn't aided by a backing track.

The Raymond v. Raymond singer tore through early favorites like "Caught Up," "You Make Me Wanna" and "U Remind Me." But when Usher went all the way back to "My Way," things really heated up. He pulled off some suggestive crotch grabs reminiscent of his idol Michael Jackson before getting down on the ground with a mic stand and doing things that would make Justin Bieber blush.

The crowd ate it up. "Love in This Club" and "Lil Freak" made the temperature rise so much that Usher had to rip off his vest, apparently forgetting that his headset mic was wired through it. He had to take a moment to unplug, the only hiccup of the night. No need to worry, the Staples Center was with him. He closed the night with "Yeah!" and current hit "OMG," while a shower of confetti rained down on the sweaty masses.