Michael B Jordan earned the best actor trophy for his dual roles as twin brothers in Sinners. Jessie Buckley won best actress for playing the wife of William Shakespeare, Agnes Hathaway, in Hamnet.
Australia's Rose Byrne missed out on the best actress award after she was nominated for If I Had Legs I'd Kick You.
Paul Thomas Anderson won his first Oscar for best director, a long-in-coming coronation for the One Battle After Another filmmaker.
Sean Penn was named best supporting actor for his role as an obsessed military officer in One Battle After Another.
It was the third Oscar for Penn, who frequently skips movie industry awards shows and was not in LA's Dolby Theatre audience.
He dashed the hopes of Australia's Jacob Elordi, who had been nominated in the supporting actor category for his performance in Frankenstein.
The 75-year-old Amy Madigan was named best supporting actress for her role as the wacky Aunt Gladys in horror film Weapons.
She earned her first Oscar 40 years after her first Oscar nomination.
In her remarks, Madigan thanked Weapons director Zach Cregger.
"He just wrote a dream part and he just let me grab it by the throat," Madigan said.
KPop Demon Hunters, a Netflix movie that became a global phenomenon, was named best animated feature.
Amid the celebration, the show took on a serious tone to honour two major losses in the film world - the directors Robert Redford and Rob Reiner.
Billy Crystal, star of When Harry Met Sally, said Reiner's films including A Few Good Men and This Is Spinal Tap would "last for lifetimes."
He was joined on stage by Demi Moore, Meg Ryan and other cast members from Reiner classics.
Barbra Streisand, who played opposite Redford in The Way We Were, called Redford a "brilliant, subtle actor" and an "intellectual cowboy." She finished her remarks by singing a few lines from the movie's well-known title song.
Host Conan O'Brien opened the festivities by joking that he was honoured to be "the last human host" of the awards at a time when Hollywood is worried about artificial intelligence taking over jobs.
The glitzy celebration, Hollywood's most over-the-top gala of the year, took place as the US wages war on Iran.
Security was tight in and around the ceremony. Organisers said they were working closely with the FBI and Los Angeles police after a federal warning of a possible Iranian threat against California, though authorities have cited no specific or credible danger to the Academy Awards.
Another Australian, Nick Cave, missed out on the original song award, which went to Golden from KPop Demon Hunters.
Cave had been nominated for the title song to Clint Bentley's film Train Dreams, starring Joel Edgerton.
with Reuters
