Since Kevin Spacey became the artistic head of London’s recently resuscitated Old Vic theater three years ago, the tonier British tabs have taken umbrage that he, of all unexpected people, had come to the rescue of this venerable English institution.

“I never got a sense anyone was critical of the fact I’m American,” he said recently. “I think the criticism was more that I’m a movie star. Even though I may be known as a movie actor more than I am as a theater actor — for anybody who really knows me and knows my career — they know I spent 20 years in theater before I ever stepped in front of a camera.”

While his naysayers may have found it disconcerting to have Lex Luther at play in the fields of Lord Olivier, Mr. Spacey has cut back on screen work to revel in his new role of theatrical kingpin, quelling his critics with the sweet smell of success.

Now his most high-profile measure is about to reach Broadway stages, as the “new Old Vic” brings its acclaimed revival of Eugene O’Neill’s “A Moon for the Misbegotten” to the Brooks Atkinson Theatre, where it will open April 9. The show stars the artistic director himself and features an actress, Eve Best, whose participation signals a further coup for Mr. Spacey in his resuscitation of the Old Vic.

Ms. Best, a Best Actress Olivier contender last month for this performance and a winner in that category last year for her Hedda Gabler, is this production’s secret weapon. She is virtually unknown in this country, save for a “Prime Suspect” guest shot earlier this year. But she is one of England’s most honored stage stars, and has, award-wise, won one of everything since arriving on the scene as Jude Law’s leading lady in “Tis Pity She’s a Whore.” That got her the London Evening Standard Award as Best Newcomer of 1999.

Ms. Best plays a pig farmer’s daughter, with whom Mr. Spacey’s character, James Tyrone Jr., falls in love. It is a character with which Mr. Spacey is intimately familiar; of his six Broadway appearances, half have been in the plays of O’Neill, and a third have been as James Tyrone Jr., the haunted alcoholic O’Neill based on his own brother. Mr. Spacey was 26 when he first played the character in Jonathan Miller’s 1987 “Long Day’s Journey Into Night”; now 47, he is reprising Jamie 11 years down the road, right on self-destructive course.

While the role may be a natural fit for Mr. Spacey, Ms. Best’s participation in the production was less of a given. She originally pursued the part because she wanted to work with Howard Davies, with whom she worked in O’Neill’s “Mourning Becomes Electra,” as Lavinia, for which the London Critics Circle named her 2003’s Best Actress. Mr. Davies is now directing “A Moon for the Misbegotten,” and directed Mr. Spacey in “The Iceman Cometh.”

“Howard is an O’Neill expert in England,” Ms. Best said. “I feel so safe in his hands because he knows what’s going on in the plays and how to portray the story as best as possible.”

Ms. Best’s role’s in “Moon” and “Mourning,” however, are polar opposites. But, Ms. Best pointed out, “what links them is that they’ve both gone through a lot of pain, but they’re different in the way they deal with it. Lavinia becomes a destroyer and avenger, and Josie is — what I love about Josie — she’s completely a life-giver. Everything about her has to do with giving and nurturing.”

But in addition to being giving and nurturing, Josie is, according to the play’s text, “a fat cow” — and Ms. Best hardly fits that bill. She may indeed be the slenderest Josie on Broadway record.

“Initially, superficially, that was the hardest thing,” she said. “I asked Howard, ‘Are we going to have a fat suit?’ He said, ‘Don’t be so absurd. It’s not about that. It’s about how she feels as a person.’ Of course, that’s true. I don’t know any woman in the world who isn’t paranoid that they’re overweight,” Ms. Best said. “Even Gwyneth Paltrow.”

Mr. Spacey also rose in defense of Ms. Best’s slimness. “Colleen Dewhurst [the Tony-winning Josie] wasn’t ‘a fat cow,’ either,” he noted. “I think what people have to do, in a sense, is kinda ignore that description. What Eve’s performance shows you is that she has convinced herself that she is a ‘fat cow.’ God knows, we all in life convince ourselves of things that aren’t necessarily true.”

Besides, Mr. Spacey said, “no single actor owns a role. We are the custodians of roles, and we have our own interpretation of it. Ten years from now, another director and another group of actors will come along and have a different interpretation — and the play will live through that interpretation That’s what makes O’Neill our Shakespeare.”