Emma Nelson, the newcomer at the center of Richard Linklater’s latest film, “Where’d You Go, Bernadette,” didn’t have the ideal introduction to her A-list co-star, Cate Blanchett.

As Nelson, now 15 years old, was sitting in the waiting area to be called for her audition, her mother had a surprise run-in with Blanchett at the restroom.

“There was a bit of a mix-up at the door where my mom forgot to hold the door and ended up closing it on her,” Nelson tells The Post, with a laugh. “So that was my first experience. Very embarrassing.”

“Where’d You Go, Bernadette,” in theaters Friday and adapted from Maria Semple’s 2012 best-selling novel, follows a Seattle mom, Bernadette (Blanchett), who gave up her illustrious career as an architect to focus on raising her daughter, Bee (Nelson). Now, as Bee readies for boarding school, Bernadette’s mental state begins to unravel and she embarks on a journey to find herself again.

The role of Bee marks Nelson’s very first on-screen. But when she got the part, Nelson, who had just finished seventh grade, couldn’t tell anyone but a few close family members that she’d landed the opportunity of a lifetime. As eighth-grade classes began, Nelson was still shooting, and her friends were in the dark.

“Everybody was like, ‘Where’s Emma? What’s going on?’ And I just had to lie,” she says.

It wasn’t until the next summer that her casting was officially announced, revealing she’d been chosen from a pool of 500 hopefuls. Nelson could finally talk about her secret double life, but she didn’t exactly get any big reactions from kids at school.

“People are like, ‘Oh, that’s so cool,’ ” says Nelson. “But they’re really confused because it’s not like a franchise or anything that they’ve heard of before.”

Nelson says that’s fine by her, as she likes to keep her two lives separate. One day she’s working with the biggest names in show business, the next she’s a typical kid gearing up for 10th grade at a public high school in a Chicago suburb.

“I’d rather just be ‘Emma’ at school,” she says. “I love the town that I’m from, and I like to go back there and just go back to my normal life.”

Nelson splits time between her parents, who are separated. Her mother owns the preschool Nelson once attended and lives in Barrington, Ill., while her father works for Comcast and is also the mayor of West Dundee, Ill. Her only sibling, Sophia, is a high school senior.

Nelson is excited to work again and is mulling college plans, but in the meantime, she’s making the most of being a teenager. She’s in a school a cappella group, she just binged the new season of “Stranger Things” and she loves listening to the indie pop artist the Japanese House.

“I know that eventually home is going to be kind of like an escape,” she says. “And I want to keep it that way.”