The pair star in The Paperboy, which follows a journalist (Matthew McConaughey) investigating the case of a death row inmate (John Cusack) accused of a crime he didn't commit.
Efron plays McConaughey's naive younger brother, who becomes involved with the inmate's penpal fiancée (Kidman).
One scene involves Efron's character Jack Jansen watching on as Cusack's character masturbates while looking at Kidman's character Charlotte Bless.
"That was the first day of filming and Nicole just completely went for it," Efron told Black Book magazine. "She was telling everyone, 'I'm bringing my A-game. What do you have?'
"I've never been so scared in my life, but that moment affirmed this movie was everything I set out to do."
Efron previously confessed that he pinched himself everyday while working with "gorgeous" Kidman.
Watch a preview clip of The Paperboy below: