It seems almost strange to see a crowd packed around a nearly empty stage — with only two small platforms and zero instruments. But half-way into the first song, you realize, you don’t miss the band at all.

Pentatonix performed Wednesday to a near sold-out crowd at Mill City Nights, showing their fans why they’re the reigning champs of “The Sing Off.”

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The group, composed of Mitch Grassi, Scott Hoying, Kirstin Maldonado, Avi Kaplan and Kevin Olusola, is simply spectacular. They are the proven product of extraordinary talent and a breath of fresh air in the era of auto-tuned and lip-synched concerts.

Sure, they may not have the stage presence of a big-time performer (it’s just a simple stage, a few well-coordinated lights and five microphones) but when they get going, their voices easily fill a venue with power and precision. (Side note: Apparently this is unless you’re watching from the second level, where there are still bugs that need to be ironed out at Mill City.)

After initial skepticism to what this kind of a capella would be like in concert-form, any doubt and any desire for added entertainment went out the window after Pentatonix performed their first song.

The crowd — perhaps one of the most diverse I’ve seen at Mill City Nights — was clearly full of diehard fans, every note, every harmony was received with screams, shout-outs and sing-alongs.

They performed a solid line-up of songs, made memorable from their season on “The Sing Off.”

(credit: CBS)

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Kicking things off with a melody mash-up and saving some of the powerhouse vocals for the end. In what Scott called his favorite song to perform — and most emotional for the group — a clear highlight of the night came from the incredible cover of Florence and the Machine’s “Dog Days Are Over.” Truly one of the best songs to showcase each member’s individual talent — from Avi’s incredible bassline, Scott’s unwavering lead vocals, Kirstie’s hot harmonies, Kevin’s ridonkulous beatboxing and yes, Mitch’s fantastic range that would make a high soprano green with envy.

The show, understandably, had a few lulls while the group rested their vocals and bantered a bit, in order to chug some much needed H20. But remember, it’s only them — there’s no room for guitar solos, drum sequences and back-up dancers busting a move to house music.

They did the best they could during these times — keeping Avi and Kevin on stage to lead a venue-wide song with audience participation or allowing Kevin to show off his God-given talent in a beatboxing solo that made everyone in the room scoff in utter fascination.

They did a few of their newly arranged YouTube hits — including Imogen Heap’s “Aha!” and yes, they encored with PSY’s “Gangnam Style.” Even if you’re sick of the viral hit, you have to tip your hat to Scott’s flawless Korean, which Kevin told me earlier he learned in record time.

And just for the fans who came to see them on tour, they mixed a couple of new jams, including a Justin Bieber-Katy Perry mash-up — which my friend called the highlight of her night.

The highlight of one audience member’s night, however, had to be when the group called her on stage for a personal serenade. Almost too perfectly, the girl’s name was Star — and she was probably the best possible random audience member they could’ve picked. From the get-go, she was Star-ry eyed and completely enthralled. The song? Marvin Gaye’s “Let’s Get It On.”

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For the diehard fan, and for newcomers, the show was fun and full of entertainment. The amount of fresh-faced talent put into one sensational group is awe-inspiring — and the fact these talents still trip over their words, joke around and remain thankful is truly refreshing.

Gallery: Pentatonix Performs