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By Lisa Richwine

LOS ANGELES, March 2 (Reuters) - "A Real Pain" star Kieran Culkin won best supporting actor at the Academy Awards on Sunday where "Anora," "The Brutalist" and "Conclave" were competing for the coveted best picture trophy.

Culkin, who started acting as a child, was honored for playing one of two cousins who travel to Poland to study their family's history.

"I have no idea how I got here," Culkin said on stage at the Dolby Theatre in Hollywood. "I've been acting all my life. I never felt like this was my trajectory."

"Anora," a story about a sex worker who gets a shot at a Cinderella story, landed the award for original screenplay. The adapted screenplay award was given to "Conclave," a movie that imagines the secret proceedings to select a new pope.

Both are considered candidates to win the top honor of the night, the best picture statuette.

The prize for best animated feature went to independent film "Flow," the first movie from Latvia to win an Oscar.

Nominees Ariana Grande and Cynthia Erivo opened the show with a "Wizard of Oz"-themed medley including the showstopping hit "Defying Gravity" from their film "Wicked."

Grande, Zoe Saldana, Selena Gomez and other stars wore shiny and sculptural gowns. Timothee Chalamet chose a canary yellow tuxedo, prompting a jab from host Conan O'Brien.

"You will not get hit on your bike tonight," O'Brien said.

O'Brien also threatened any winners who spoke too long that he would show their old headshots or cut to a shot of actor John Lithgow "looking slightly disappointed."

This year's Oscars race has featured twists and turns, and no movie has dominated the precursor film awards.

Any of three films could score best picture, according to Oscars pundits. They are "Anora," "Conclave" and "The Brutalist" about a Jewish immigrant and architect chasing the American dream.

Others in the best picture field include blockbuster musical "Wicked," a prequel to "The Wizard of Oz," and "A Complete Unknown," the Bob Dylan biopic starring Chalamet.

Netflix NFLX.O musical "Emilia Perez" headed into the ceremony with the most nominations. But its chances of victory dwindled when offensive social media posts surfaced from star Karla Sofia Gascon. The actress, the first openly transgender person nominated for an acting Oscar, disappeared from the awards circuit but attended Sunday's ceremony.

Winners of the gold Oscar statuettes are chosen by the roughly 11,000 actors, producers, directors and film craftspeople who make up the Academy of Motion Picture Arts and Sciences.

Best actor could go to either Chalamet or "The Brutalist" star Adrien Brody, according to awards experts.

Brody became the youngest best actor winner when he landed the prize at age 29 for "The Pianist" in 2002. Chalamet is nine months younger than Brody was at the time.

Best actress is widely expected to go to Moore for "The Substance," though one pundit said the category could produce an upset win for Brazil's Fernanda Torres of "I'm Still Here." The academy has increased its international membership, which could favor Torres, said Ian Sandwell, movies editor at Digital Spy.

"She could well be a surprise and the only one to take it away from Demi on the night," Sandwell said.

(Reporting by Lisa Richwine; Editing by Mary Milliken and Howard Goller)

((lisa.richwine@thomsonreuters.com; Follow me on Twitter @LARichwine; 1-424-434-7324))