NEW YORK — Grace Potter is in the middle of an electrifying concert with her band, the Nocturnals, performing retro-rock grooves from their breakthrough album, when she takes what seems like a surprising detour and launches into a Beyonce song.

“Why don’t you love me? Tell me, baby, why don’t you love me?” Potter howls as she does a rendition of the Beyonce jam so pitch-perfect she seems to have morphed into the diva.

She’s wearing a minidress and stiletto heels that Beyonce might rock, shaking her long blond hair from side to side. The only big difference between the two singers: Potter has a guitar strapped around her body.

It has taken years for Potter to release her inner Beyonce, but it’s a transformation that Potter felt was necessary if she and the Nocturnals were going to fully realize their rock ‘n’ roll dreams.

“I think part of my growing up and part of my improvement as a frontwoman was finally embracing that spirit and that animal instinct to own it up there,” says Potter, speaking backstage before the band’s recent capacity-crowd concert at New York City’s Irving Plaza.

“It took a lot of years for me to get comfortable, strutting my stuff, dancing like a fool, having that sparkly dress on that says ‘here I am,’” she acknowledges. “Because in the beginning, I was scared — I was scared that I wasn’t going to be taken seriously.”

It’s hard not to take Potter seriously now. The band has had a breakthrough year since the release of their self-titled album last summer,  and the 27-year-old Potter, as the Nocturnals’ sexy-glammed up frontwoman, is poised for her own star-making turn.

“If you’re looking at female artists, there are very few emerging right now that do what she does,” says Rick Krim, VH1’s executive vice president, talent and music programming. “She’s got an amazing voice, and a great stage presence. She’s fun, she’s entertaining and she’s got a great personality. It’s a great package.”

VH1 picked the Nocturnals as one of the acts to watch last year, and promptly added them to its “VH1 Divas Salute the Troops” concert in December. The group’s performance of their sultry single “Paris (Ooh La La)” riveted the crowd; album sales increased 113 percent after the concert aired, VH1 said.

This summer, the band’s profile will continue to rise. The Nocturnals are booked for major festivals this summer, including their first appearance on the main stage of the Bonnaroo Music & Arts Festival in Manchester, Tenn. They are also planning their own festival, Grand Point North, in Burlington, Vt.

“It’s exciting. We’ve been planting seeds for about eight years,” said drummer Matt Burr. “It was the perfect storm of songs getting better and touring more and more and more. … Everything kind of really hit perfectly.”

Potter, from Waitsfield, Vt., met Burr and fellow guitarist Scott Tournet when she was a college student and working on her first album, 2004’s “Original Soul.”

Burr remembers the first time he heard Potter sing. She was at a coffeehouse, and she played an original tune: “Apologies.”

“I saw her play it at an open mike, I was one of many who was in attendance with my jaw on the floor,” said Burr.

He and Tournet quickly signed on to work with Potter, appearing on her album, and a year later, they released their first album as Grace Potter & the Nocturnals, “Nothing but the Water.”

Back then, Potter had many of the same qualities that make her so refreshing today: a husky, soulful voice, a deft skill as a keyboardist, good looks and a spark during her performances. But she was a brunette, more apt to wear jeans and a T-shirt during a performance, in contrast to her model-like persona today.

As the female leader of a band, Potter was unusual. She recalls when she’d be mistaken as the manager of the band, or one of their girlfriends. So she resisted dressing in feminine gear, though she was a fashionista at heart. She also felt pressure to prove herself as a female musician.

“I worked extremely hard at my craft and at being a good songwriter, being a good guitar player, being a good organist because I didn’t think people would take me seriously,” she says. “I was so focused on convincing people that I was one of the guys, so it was weird for me. … It was tricky.”

She no longer has those worries. These days, she looks like a cover girl with her sleek tresses, sexy outfits and stilettos (she even wears them during sound checks).

Not everyone is happy with her transformation. Some point to old photographs of a dark-haired Potter dressed in flannel and jeans and wonder whether she made a calculated move to change her look for more attention.

Changing her look was calculated — but not for more mainstream appeal. Potter says it was the culmination of the band’s ramped-up new sound — and her new attitude. She is more determined to give her stage show everything — including strapping on high heels and learning to play the guitar.

“It wasn’t just, ‘Hey, I wanna dress up cute now,’ it really was from the bottom up a sense of production. Just like you would spend time making the lights perfect onstage, or the backdrop perfect onstage, what we put on our bodies needs to reflect the music, so the fashion has been a really fun new part of the production of the show because it is a show,” she says.

“It naturally happened, which was so great. We went from wearing flannels and mud boots but flicking the switch and really amping it up,” says Burr. “It’s healthy to change and grow. … She just naturally sort of progressed into the best sense of the word diva.”

Part of Potter’s revitalization came as the band was at a crossroads two years ago. Her bass player had left, and Potter set out to record a solo record with renowned producer T Bone Burnett.

The band was thinking about going on hiatus, but instead, starting working on new music while on the road with two new members: bassist Catherine Popper and rhythm guitarist Benny Yurco.

“I didn’t realize how much sonic change was going to be in that until I saw it, until I heard it on the records, and as we started playing music together, the musicality really did improve dramatically,” Potter says.

Their record label urged them to go into the studio with their new rocking sound, so she put the Burnett album in the vault. The Nocturnals’ third album continues to gain steam as it reaches the one-year mark, and Potter’s glow gets more luminous.

Despite all her success, she still has a few naysayers. When she met one of her childhood idols, she was a bit dismayed when the female singer-songwriter started questioning Potter’s look.

“This whole sexy thing you’re doing, I mean — you can’t keep it up, you can’t do that forever. Don’t you want to be taken seriously as a songwriter?” Potter remembers the woman asking her. “‘How do think you’re going to do this when you’re 50 and you’re still trying to be in the mini-dresses?’”

Potter didn’t skip a beat with her retort.

“I’m like, ‘What the [expletive] do you think Beyonce’s going to be doing, tell me that? Because she’s got it going on!’”