Los Angeles, California - Vatican thriller Conclave won top prize at an unpredictable Screen Actors Guild Awards gala Sunday, throwing a potential late curveball into the Oscars race just a week before the Academy Awards.

The movie about the mysterious, behind-closed-doors selection process for choosing a new pope won the prize for best cast – the SAG equivalent to best picture – for a stellar ensemble including Ralph Fiennes, Stanley Tucci, John Lithgow, and Isabella Rossellini.

Collecting the award, Fiennes said the win was a celebration of "community," and "the supreme importance of it in our work and in the world."

Rossellini earlier wished "a quick recovery" to Pope Francis, who has been in hospital for 10 days with respiratory issues and remains in critical condition.

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Having also won big at Britain's recent BAFTA awards, Conclave now appears a strong, late-breaking contender for the best picture Oscar, alongside critical darlings such as Anora.

In another upset, Timothee Chalamet won the SAG Award for best actor for his portrayal of a youthful Bob Dylan in A Complete Unknown.

"I know we're in a subjective business but the truth is, I'm really in pursuit of greatness," said Chalamet, never short on confidence.

"I know people don't usually talk like that, but I want to be one of the greats," he added, citing inspirations including multiple Oscar winners Daniel Day-Lewis and Marlon Brando, and sporting titans Michael Jordan and Michael Phelps.

"I want to be up there," said the 29-year-old.

Adrien Brody has long been seen as the runaway favorite for this year's awards season with his performance as a brilliant architect, haunted by the Holocaust, in The Brutalist.

Chalamet's win suggests that the Oscars race could be closer than expected.

The SAG Awards are voted on by Hollywood actors, who represent the biggest branch of the membership of the Academy of Motion Picture Arts and Sciences, which votes for the Oscars.

The prizes are closely watched as indicators of who is likely to win Academy Awards.

More closely following pundit predictions Sunday, Demi Moore won the best actress SAG Award for her role in gory body horror The Substance.

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Moore's role as an aging celebrity who injects a serum to temporarily reclaim her younger body – with disastrous consequences – has marked a stunning career renaissance for the 1990s megastar.

Acting "changed my life because it gave me meaning, it gave me purpose and it gave me direction, because I was a kid on my own, who had no blueprint for life," she said.

Kieran Culkin and Zoe Saldaña won the best supporting actor and best supporting actress awards for A Real Pain and Emilia Perez, respectively, at the gala aired on Netflix.

Culkin plays an emotional and charismatic tourist retracing his ancestral roots in Poland with his mismatched, neurotic cousin (Jesse Eisenberg).

Saldaña portrays a lawyer hired to help a Mexican cartel boss undergo gender reassignment surgery in the scandal-hit Netflix film Emilia Perez.

Both have won nearly every prize in their categories at multiple shows this year, and appear to be shoo-ins for the Oscars next Sunday.

Jane Fonda received the union's Life Achievement Award, using much of her speech to urge Hollywood to "fight back" against the current state of US politics.

"A whole lot of people are going to be really hurt by what is happening, what is coming our way," warned Fonda.

While not directly mentioning President Donald Trump, Fonda notably name-checked Sebastian Stan's performance as Trump in the movie The Apprentice.

Comparing the present situation to the intolerance of the McCarthyism of the 1950s, Fonda said, "Today, it's helpful to remember... that Hollywood resisted."

Her comments, greeted with a standing ovation from the audience, came at a time when Hollywood studios have been criticized for falling in line with White House policies such as the shuttering of diversity hiring programs.

In the television awards, Japanese period drama Shogun won best ensemble and best stunt ensemble, while its stars Anna Sawai and Hiroyuki Sanada won individual awards.

In comedy, Martin Short won for best actor for Only Murders in the Building, which also won the best ensemble prize, while Jean Smart won for Hacks.