Director Bong Joon-Ho reacts after winning the Palme d'Or award for "Parasite" on stage during the Closing Ceremony of the 72nd annual Cannes Film Festival on May 25, 2019 in Cannes, France.

South Korean thriller "Parasite" was the upset winner at the Screen Actors Guild awards on Sunday, while Joaquin Phoenix and Renee Zellweger were named best actors, cementing their roles as frontrunners at the Oscars next month.

"Parasite," the Korean language social satire about the wealth gap in South Korea, beat homegrown Hollywood movies with A-list casts "The Irishman" and "Once Upon a Time in Hollywood" to take the top prize of best movie ensemble cast.

Winning the award, director Bong Joon Ho said it made him think that "maybe we haven't created such a bad movie."

"I am so honored to receive this award. I will never forget such a beautiful night," he said through an interpreter.

The SAG awards, which focus entirely on performances, are closely watched as an indicator of Oscar success because actors form the largest voting group in the Academy of Motion Picture Arts and Sciences.

Phoenix's terrifying performance as a loner who finds fame through violence in "Joker" has swept awards season.

"I am standing on the shoulders of my favorite actor - Heath Ledger," Phoenix said on Sunday, referring to the actor who won a posthumous Oscar in 2009 for his turn playing the comic book villain.

Zellweger, likewise, has picked up most of the prizes so far for her performance as a desperate, aging Judy Garland in biopic "Judy."

Brad Pitt picked up another trophy for his supporting role as a charming stunt man in "Once Upon a Time in Hollywood," while Laura Dern was named best supporting actress for playing a ruthless divorce lawyer in Netflix domestic drama "Marriage Story."

"It was a difficult part," quipped Pitt of his role. "A guy who gets high, takes his shirt off and doesn't get on with his wife. It was a big stretch," he said to laughter, riffing on his own life as a twice-divorced Hollywood heartthrob.