The “Modern Family” actor stepped into a role originated by Spader on Broadway for a special online performance of the David Mamet play “Race.”

“I’ve been friends with Dave Mamet since 1980,” O’Neill told The Post. “We met in New York all that time ago. I’ve done several plays with him over the years and I got a call from his Girl Friday.”

The theatrical event, directed by Phylicia Rashad and also starring David Alan Grier, is being held online only — much to the 74-year-old actor’s confusion.

“I didn’t even know what they were talking about,” he said. “How do you do a play on Zoom? But she said, ‘It’s for charity and James Spader couldn’t do it and Dave suggested you.’ ”

It turns out O’Neill is kind of a novice when it comes to his computer, admitting it “was not easy to do at all.

“I thought it would be a staged reading but in this case, they said, ‘No, we want you in your costumes and looking like you’re not reading it.’ ”

The actor spoke to The Post from his house in Hawaii where he has been holed up since March. When asked if the home was paid for with “Married with Children” or “Modern Family” moolah, he replied with a laugh, “Both!”

“Race,” which benefits the Actors Fund, premieres on Broadway’s Best Shows Thursday, Oct. 29 and will be available until Monday, Nov. 2.

To learn more about the Spotlight on Plays series, visit Broadway’s Best Shows Spotlight on Plays.