Carey Mulligan, the 24-year-old star of “An Education,” prepared herself for Oscar nominations in a peculiar way: She watched a film about drug addiction: “Requiem for a Dream.”

First, the nominee for best actress went out to see Mel Gibson’s “Edge of Darkness”; then she stayed up late at home watching the harrowing “Requiem,” hoping it would distract her.

“It was so trippy,” the British actress said Tuesday in an interview from Los Angeles. “It gave me something else to think about.”

But the reality couldn’t be avoided for long: Mulligan’s widely acclaimed, star-making performance had brought her all way to the Oscars.

“It was like a really good, friendly punch in the stomach,” she said. “It’s a good feeling, but it’s like a jolt. You can be in as many top-five lists and have as many people say things to you on red carpets as you like, and it doesn’t for a single second make you honestly think that you’re going to get nominated.”

In “An Education,” Mulligan plays Jenny, a teenage schoolgirl in suburban 1960s London who questions her imminent and promising ascent to university when she falls in love with an older man (Peter Sarsgaard). As Jenny, Mulligan is a seldom seen combination of beauty and smarts — there isn’t a man or adult who intimidates her.

“She’s got so much going on in those eyes, in the face — the animation, the intelligence,” said Nick Hornby, author and screenwriter of “An Education,” who was nominated Tuesday for best adapted screenplay. The film was also up for best picture.

“I used to joke to people that one line we were never going to get in a review was, ‘This is a great movie, but unfortunately Carey Mulligan sucks,’” said Hornby. “Without her, we were completely sunk. There’s a radiance about her.”

The performance has brought countless comparisons of Mulligan to Audrey Hepburn. She is also nominated for her first Oscar at the same age Hepburn was for hers — 1953, for “Roman Holiday,” which she won.

“I’ve always been so embarrassed by that comparison,” says Mulligan. “You feel like Shrek compared to Audrey Hepburn. It’s a really nice comparison, but it just seems so mad.”