Chris Brown breaks down at awards show

Chris Brown performs a tribute to Michael Jackson at the BET Awards in Los Angeles. (AP Photo/Matt Sayles)

Kanye West opened the show in his first TV appearance since dissing Taylor Swift at last year's MTV Video Music Awards. T.I. made a triumphant return to TV for his first performance since being released from prison in December.

And 1980s hitmaker El DeBarge blazed back onto the stage to play old hits and the title track from his first new album in 16 years.

But most unexpected was Chris Brown, who offered an emotional tribute to Michael Jackson.

The embattled pop star has mostly kept a low profile since pleading guilty to felony assault for beating up Rihanna in February 2009.

But here he was, centre stage, mimicking Jackson's signature dance moves with almost eerie accuracy. Introduced by Jermaine Jackson, Brown embodied the King of Pop, wearing his fedora and spangled glove and moonwalking across the stage to "Billie Jean."

Then, as Brown grabbed a microphone to sing "Man in the Mirror," he broke down in tears. His voice cracked, he couldn't sing, and at one point he crumpled to the stage in apparent agony. It was a moving moment made even more so by the song's lyrics and his own recent past.

The 21-year-old returned to the stage later to apologize to his fans.

"I let you all down before, but I won't do it again. I promise you," Brown said.

Performances were so plentiful during the 3 1/2-hour show that prizes were almost secondary.

Usher was backed by a string section as he sang "There Goes My Baby." Drake, who was named best male hip-hop artist, performed a medley of his hits. B.o.B. was joined by Keyshia Cole, and later Eminem, on "Airplanes."

Eminem continued with his new single, "Not Afraid," backed by a choir. Trey Songz, who was named best male R&B artist, crooned his hit, "Yo Side of the Bed," as a banner on stage behind him read, "pray for our soldiers and their families."

Alicia Keys performed a medley of her hits, bookended by two awards. She won for female R&B artist and best collaboration for her song with Jay-Z, "Empire State of Mind."

Ludacris was surrounded by female violinists and backed by Tommy Lee on drums as he performed "My Chick Bad." Then a marching band joined him on stage - as did DJ Khaled, T-Pain, Rick Ross and Nicki Minaj - for the rousing "Hands Up."