LOS ANGELES (Reuters) - Lupita Nyong'o won the best supporting actress Oscar on Sunday for her first film role ever as the slave, Patsey, in the drama "12 Years a Slave," a big recognition for one of the films favored to win the top honor of the night, the Academy Award for best picture.
Its biggest competitor for best picture, space thriller "Gravity" from Mexican director Alfonso Cuaron, racked up five Oscars for technical achievements like visual effects and cinematography, a reward for its groundbreaking work on conveying space and weightlessness.
Nyong'o's win over Jennifer Lawrence for her role as a loopy housewife in "American Hustle" injected some drama halfway through the 86th Academy Awards, after early Oscars went to heavy favorites.
Jared Leto won best supporting actor for his role as a transgender woman in "Dallas Buyers Club" and the tale of Nordic princesses, "Frozen," won best animated film, a first for Disney Animation Studios (DIS.N) since the category was introduced in 2002.
Comedian and talk show star Ellen DeGeneres returned as Oscar host on Sunday in an appearance many saw as calculated to project a lighter, more affable tone for Hollywood's biggest night after the provocative performance of her immediate predecessor, Seth MacFarlane.
She mixed with the star-studded crowd, taking selfies with the likes of Brad Pitt and Angelina Jolie, and showed in her opening monologue she was not above poking fun at some of the film industry's biggest names.
Leto, who returned to acting from a six-year break in the low budget AIDS drama, "Dallas Buyers Club," injected a serious note into the show in his acceptance speech, paying tribute to all those who have died from the worldwide HIV epidemic.
"This is for the 36 million people out there who have lost the battle to AIDS," Leto said.
Leto also brought international political unrest into the Dolby Theatre by voicing his support for protesters battling their governments in Ukraine and Venezuela.
In accepting the first award of the night for "12 Years a Slave," Nyong'o, 31, paid homage to her character, a hardworking slave who suffers great abuse in the story based on the memoir of free man turned slave Solomon Northup.
"It doesn't escape me for one moment that so much joy in my life is thanks to so much pain in someone else's, and so I want to salute the spirit of Patsey, for her guidance," a tearful Nyong'o told the audience.
In one of the strongest years for film in recent memory, the 6,000-plus voters of the Academy of Motion Picture Arts and Sciences were expected to scatter golden Oscar statuettes widely among the many acclaimed movies in contention.
Sunday was the culmination of an unusually long awards season, extended by the Winter Olympics, and for many of the nominees it spelled the end to months of campaigning and years of work on a film.
Bedecked in gowns, tuxedos and even shorts, the world's top actors and actresses strode down the red carpet right after the sun broke through four days of heavy rain that threatened to put a damper on Hollywood's biggest night.
In a sea of shimmering metallics and bold jewel tones, the fashion darling of the awards season, Nyong'o, won over the most high-stakes red carpet of them all.
The Kenyan actress wore a custom halter-neck pastel blue Prada gown which she helped to design, saying it was inspired by champagne bubbles and a color that reminded her of Nairobi.
Nyong'o's co-star, British best actor nominee Chiwetel Ejiofor, the film's main protagonist, showed up in the classic tuxedo, while singer Pharrell Williams wore a Lanvin tux with shorts rather than trousers.
The Academy could make history this year if were to choose "12 Years a Slave" for best picture. It would be the first time that the top film honor goes to a movie by a black director in the 86 years of the Oscars.
DeGeneres joked about the weighty decision ahead in one of her more daring lines.
"Anything can happen, so many different possibilities," she said. "Possibility No. 1, '12 Years a Slave' wins best picture. Possibility No. 2, you're all racists."
Among the other best picture contenders is 1970s period crime caper "American Hustle" from director David O. Russell, which scored 10 nominations. For the second year in a row, Russell has achieved the rare feat of having his actors nominated in all four acting categories. Martin Scorsese's "The Wolf of Wall Street," a tale of financial greed and excess, has also been a hit with audiences and critics.
A total of nine films are competing for best picture, including Somali piracy thriller "Captain Phillips," the adoption drama "Philomena," the heartland comedy "Nebraska," the computer-age romance "Her," and "Dallas Buyers Club."
Cate Blanchett was heavily favored to win her first best actress Oscar for her portrayal of the disgraced socialite in Woody Allen's "Blue Jasmine."
Matthew McConaughey was also a solid bet for best actor for his role as the unlikely AIDS activist in "Dallas Buyers Club," for which he lost some 50 pounds (23 kg).
Additional reporting by Piya Sinha-Roy, Eric Kelsey and Lisa Richwine; Editing by Sandra Maler