"I am floored. Wow," she said, thanking Bieber and his manager, Scooter Braun.
Party girl Ke$ha was glammed up on the red carpet, rocking long, flowy blonde hair and a light pink dress. She switched to her normal attire when she performed her hit single "Die Young." It was tribal, with shirtless dancers in skin-tight pants, silver hair and skeleton-painted faces, who also played the drums. Ke$ha was pants-less, rocking knee-high boots and rolling on the floor as she finished up the song.
Minaj and Christina Aguilera were blonde bombshells, too: Minaj's hair was busy and full of volume and she sported a neon strapless gown to accept her first award. Aguilera wore a blonde bob in a purple dress that matched her eyeshadow.
Aguilera performed a medley of material from her new album and joined Pitbull onstage.
Kelly Clarkson also hit the stage, making a nod to her "American Idol" roots with a number on her dress and three judges looking on as she sang "Miss Independent." Then she went into "Since U Been Gone," ''Stronger" and "Catch My Breath."
Fellow "Idol" winner Carrie Underwood won best favorite country album and performed, hitting the right notes while singing "Two Black Cadillacs." She talked about singing competition shows backstage.
"These people that go on these shows are so talented, you know? And I would love to see if so many of the other artists that are out there today would go back and try out for these shows, because they might get their behinds kicked by some of the contestants," she said.
Luke Bryan won favorite country male artist and Lady Antebellum favorite country group.
American Music Awards nominees were selected based on sales and airplay, and fans chose the winners by voting online. At this award show, even the stars were fans: Pink said on the red carpet that she'd like to collaborate with Lauryn Hill. Cyndi Lauper said her musical playlist includes Pink and Minaj. Boy band The Wanted said they were excited to see PSY and Colbie Caillat wanted to watch No Doubt.
"What makes the American Music Awards special is the fans choose the winning artists," said Chester Bennington of Linkin Park, who won favorite alternative rock artist and performed "Burn It Down," as Brandy sang along and Gwen Stefani, Usher and Phillip Phillips bobbed their heads.
David Guetta won the show's first-ever electronic dance music award. Non-televised awards went to Katy Perry for pop/rock female artist, Beyonce for soul/R&B female artist, Adele for adult contemporary artist and Shakira for Latin artist.
Along with Rihanna, Minaj was the top nominee with four nominations.
AP Entertainment Writer Sandy Cohen contributed to this report from Los Angeles.
Follow Mesfin Fekadu on Twitter at http://twitter.com/MusicMesfin