How many stars can really say they let their hair down for their breakout movie role?

“I kind of didn’t believe it; it was like too good to be true,” MacKenzie Mauzy said of her fairy tale experience playing the famously long-locked Rapunzel in Disney’s “Into the Woods,” which opens Christmas Day.

Landing the storybook role in the movie musical was a “dream,” given how things began.

Mauzy, 26, told the Daily News that she first auditioned for the part of Cinderella. But the glass slipper didn’t fit, and the plum role went to Anna Kendrick.

Yet Mauzy brought a bit of magic to the audition. “They were looking for (Kendrick) first, but director Rob Marshall saw the tape and then brought me back in for Rapunzel,” she recalled.

Marshall told The News that he recognized the “vulnerability” and “emotion” Mauzy could bring to Rapunzel after she read just one line.

“My hope with casting, my philosophy is you have to make no decisions at all because someone comes in and claims the role and they bring it to life like you can’t quite imagine,” Marshall said. “I just thought, ‘There’s Rapunzel!’ ”

Mauzy, a native of North Carolina who now calls New York City home, boasts experience on Broadway, in “A Tale of Two Cities,” and in the soap opera “The Bold and the Beautiful.” Now she’s ready for her starring turn on the silver screen, hair extensions and all.

“They wanted to use my hair. The top is my hair and they just braided it into the extension,” she said of her on-screen coiffure, which she called “a tripping hazard.”

“There were pretty extensions and then there were stunt ones that people climbed!” she added. “There was a full day of climbing hair and I was like hooked in. I could not get out of it unless I had assistance.”

When Mauzy’s Rapunzel finally let down her hair (and extensions) it certainly weighed her down — but nothing could have grounded the young actress enough to prepare her for the moment when she realized she’d be acting opposite Meryl Streep, a three-time Oscar winner.

“You know you hear Meryl Streep plays your mom and you don’t exactly think, ‘Oh yeah, I got this,’ ” Mauzy joked. “I have obviously looked up to Meryl and respected her for a long time, so that was just sort of surreal — at least for me, it was a dream.”

And Streep was nothing like the witchy mom she plays in the movie, Mauzy said.

“She is very aware of the affect she has in a room that people are like, ‘Oh my God, that’s Meryl Streep,’ ” Mauzy recounted. “There was a certain time where she was like a mom character to me (off set), like she was making comments about what I was ordering at restaurants. She was sort of playing that role a little bit in public.”

Filming the music-powered scenes with Streep was, Mauzy said with emotion, “the best day of my life.”

“There was something about it in the moment, obviously because it is her, but there was always a sense of openness to trying this other way of doing it, depending on how it felt,” she said of their artistic give-and-take.