Emcee Megan Mullally kicked off the awards by tweaking their role among the many honors leading up to next month's Oscars. The 71-year-old Close, a seven-time nominee but never an Oscar victor, won best actress for her performance in "The Wife".
The cast of Black Panther accept the SAG award for best movie.
For best actor, Rami Malek's star-making turn as Queen frontman Freddie Mercury in "Bohemian Rhapsody" was rewarded - over Christian Bale's work in another biopic, as former United States vice president Dick Cheney in "Vice".
Emily Blunt meanwhile pulled off a major upset, winning the statuette for best supporting actress for "A Quiet Place", an innovative horror film directed by her husband and co-star, John Krasinski. Actors make up the largest percentage of the academy, so their preferences can have an especially large impact on the Oscar race. So my wish for all of us is: "Let's stay playful".
"If you get to experience that, you will be a fulfilled artist", Boseman wrapped up by promising a sequel: "One thing that I do know - did it change the industry? - is that you can't have a Black Panther now without a "two" on it". "It may never have been more urgent to see the world through another person's eyes than when a culture is divided so sharply".
The SAG Awards are generally considered one of the most reliable bellwethers of the Academy Awards, with best picture winners at the Oscars almost always winning the corresponding SAG award earlier in the year. Both films landed 10 Oscar nods Tuesday.
Female Actor In A Leading Role In A Motion PictureGlenn Close, The Wife Emily Blunt, Mary Poppins Returns Olivia Colman, The Favourite Lady Gaga, A Star Is Born Melissa McCarthy, Can You Ever Forgive Me? She called the SAGs "the greatest honor an actor can receive this weekend".
The 25th Screen Actors Guild Awards (SAG) Awards will air on Sunday night.
The show opened with thunderous applause for The Cosby Show actor, Geoffrey Owens.
Among the other winners was Darren Criss, who has had a dream run through awards season and took out outstanding performance by a male actor in a miniseries or television movie, beating a formidable line-up including Antonio Banderas, Bill Pullman, Hugh Grant and Anthony Hopkins. Reunited as presenters were "Fatal Attraction" stars Michael Douglas and Glenn Close.