Eighteen-year-old Justin won favourite pop/rock male artist in the first award handed out on the night and gave a broadside to those who did not think he would last on the music scene.
"I want to say this is for all the haters who thought that I was just here for one or two years. I feel like I'm going to be here for a very long time," he said, also thanking his mother, manager, family and his "beautiful, beautiful fans".
Justin also won favourite pop/rock album for Believe. He gave a stripped down, acoustic performance of As Long As You Love Me, sitting down as someone played the guitar.
He transitioned to the dance-heavy Beauty And A Beat, where Nicki Minaj joined him onstage, grinding with the teen for a few seconds. Nicki repeated her AMAs wins from last year, picking up trophies for favourite rap/hip-hop artist and album for Pink Friday: Roman Reloaded.
Usher kicked off the three-hour show with green laser lights beaming onstage as he performed a medley of songs, including Numb, Climax and Can't Stop, Won't Stop, which featured a smoky floor and a number of backing dancers, as Usher jammed all in black, with the exception of his red shoes.
The night's most colourful performance was provided by South Korean rapper Psy and MC Hammer who joined forces on the global hit Gangnam Style. Psy rocked trademark " Hammer" pants as they danced to his song and to Hammer's Too Legit To Quit.
Carly Rae Jepsen, who performed early in the night, won favourite new artist. "I am floored. Wow," she said.
Taylor Swift won her fifth consecutive award for favourite country female artist. "This is unreal. I want to thank the fans. You guys are the ones who voted on this," she said. Luke Bryan won favourite country male artist and Lady Antebellum favourite country group.
Taylor gave a masquerade-themed performance of the pop song I Knew You Were Trouble.