Rihanna, Timberlake, big winners at MTV Video Music Awards

Teenage R&B star Rihanna and pop sensation Justin Timberlake were the big winners at the MTV Video Music Awards Sunday, in a star-studded evening that saw Britney Spears make her stage comeback.

Rihanna picked up the most-sought-after Video of the Year award and Monster Single of the Year for her "Umbrella," notably beating R&B starlet Beyonce, Timberlake, rapper Kanye West, British soul singer Amy Winehouse.

"Wow. Video of the Year. This was definitely the most important one for me of the night ... the most unexpected for me," Rihanna said, accepting the top Moonman, as the astronaut-themed statuettes are known.

Timberlake, whose "What Goes Around ... Comes Around" reached number one in the US charts earlier this year, picked up the Male Artist of the Year award.

"It's just exciting to see a new generation of artists really doing it and doing it well," he said. "I think music is in a great place right now because we're all doing what we want to do. So thank you for this award MTV."

Despite not even being nominated for an award, all eyes had been on Britney Spears ahead of the 24th annual MTV Video Music Awards, being held this year at the Palms Casino Resort in Las Vegas.

The pop princess looked visibly out of shape as she opened the evening, appearing on stage at a major event for the first time in three years, since when she has had two children and gone through a string of personal problems.

The pop diva marked her comeback with "Gimme More" from her upcoming fifth album, set for release in November.

Opening with the line "It's Britney, Bitch," Spears performed in a dark sequined bikini and below the knee black boots and ended her performance perhaps appropriately with the lyric: "I just want more."

Other notable appearances of the evening were a risque introduction by comedian Sarah Silverman and performances by Alicia Keys, Chris Brown, Foo Fighters, Timberlake and Kanye West.

Underground Chicago foursome Fall Out Boy picked up the Best Group Award, as expected, beating alternative metal fivesome Linkin Park, modern rockers Maroon 5, indie/hip-hop band Gym Class Heroes and Detroit rock duo The White Stripes.

"We know that a lot of people tune into these awards to see who's wearing underwear, who's not, who's going to be a train wreck, but we want to thank all the people who are real fans of music out there," the band's Pete Wentz said.

British newcomer Amy Winehouse had been tipped for the Best New Artist Award, but lost out to New York crossover band Gym Class Heroes.

Winehouse, most recently in the news for canceling a string of US and European gigs for health reasons as she reportedly tries to beat a serious drink and drug problem, was up for three gongs but failed to score.

She had been due to perform on Sunday but canceled last month.

It was also a disappointing night for Beyonce, who was nominated for seven awards but had to settle with Most Earthshattering Collaboration, which she shared with Colombian-born pop singer Shakira.

Black Eyed Peas vocalist Fergie picked up the Female Artist of the Year but failed to show up to accept the award.

The organizers had shaken up this year's ceremony with a number of new awards, hoping to win back viewers after seeing numbers slump in recent years.

Perhaps the most unusual new award was the Quadruple Threat of the Year Award, in recognition of artists' work off stage. The award went to Timberlake, who has a number of restaurants and a clothing line.

Started in 1984, the MTV awards were originally launched to challenge the more traditional Grammy awards.

Among the more controversial episodes during that time, Madonna kissed Britney Spears and Christina Aguilera live on stage during the 2003 show.