When Josh Groban spoke to us last week about preparing for his tour opener, he noted the challenge of finding ways to fill an arena space with energy.

Mission accomplished.

Thursday night, Groban and tour mate Idina Menzel launched their monthlong jaunt from Infinite Energy Arena in Duluth (which prompted a witty aside from Groban about Duluth Trading Company underwear – and yes, he knows they’re based in Minnesota) and a dazzling three hours of vocal prowess was born.

Yes, there were a few misfires, as is expected on the first night of a major outing. Menzel missed her cue to join Groban for a couple of duets – she was in the bathroom, she explained with her trademark tart wit when she dashed out a few minutes later – and the lighting during Menzel’s opening set was a frustrating dark wash of purple and shadows.

But their voices – separately and together – provided a flawless sonic experience.

Groban, shaggy-haired and bespectacled, arrived on stage at 9:30 p.m. backed by a 14-piece orchestra and five-member band and dove into “Bigger Than Us,” from his current album, “Bridges.”

His catalog has expanded to the point of surely leaving out someone’s favorite, but he wisely sandwiched his new opener and another fresh track, “Symphony,” with his 2008 hit, “You Are Loved (Don’t Give Up).”

Though his stage is vast, it appealed with elegant simplicity. A backdrop superimposed close-ups of the singer-songwriter-actor against sheet music and other designs, while color-changing illuminations that looked like lightsabers see-sawed from the ceiling following Groban’s warm take on a gorgeously soaring “Pure Imagination.”

Josh Groban strikes a balance between sensitive and powerful as he sings at Infinite Energy Arena in Duluth at the Oct. 18 tour opener. Photo: Melissa Ruggieri/AJC

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A few songs into the set, Groban popped up on a secondary stage at the back of the arena, showcasing his piano chops in an instrumental that dovetailed into his rendition of Billy Joel’s incisive “She’s Always a Woman.”

Menzel – post bathroom run – joined him on the small stage for a stunning duet of “Falling Slowly” from the movie/musical “Once,” their voices like interlocking puzzle pieces. Groban remained for another Broadway staple, “Bring Him Home,” the potent ballad from “Les Miserables” that benefitted from the chameleonic ability of Groban’s voice.

His band played a sublime percussion interlude as Groban jogged back to the main stage for the flamenco guitar-heavy “Musica Del Corazon,” proving that in any language, he’s a magnificent singer.

Groban has always engaged effortlessly with his audiences, and age hasn’t quelled his tendencies. He spoke about the importance of arts education in schools; explained his and Menzel’s contribution (“Lullaby”) to fellow Broadway star Laura Benanti’s upcoming charity album to benefit organizations helping to reunite and support families separated at the border (“No matter your politics, there are certain things we shouldn’t do to children or families,” Groban said); and dedicated the touching new “River” to “anybody who struggles silently.”

His sensitivity is appreciated and his commitment to spotlighting others’ talents – the Georgia Boy Choir joined him for “You Raise Me Up” and “Bridge Over Troubled Water” – is commendable. Seventeen years into his career, Groban’s buttery voice and winning presence continue to impress.

Idina Menzel traveled her Broadway and movie soundtrack career during her opening set. Photo: Melissa Ruggieri/AJC

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Menzel’s opening hourlong set was equally captivating from a musical standpoint – if only, as previously mentioned, she could have been seen a bit better.

Adroitly mixing her Broadway bonafides – “The Wizard and I” (“Wicked”), “Don’t Rain on My Parade” (“Gypsy”) – with her movie credentials ( “Do You Want to Build a Snowman” from “Frozen”) and her underappreciated original solo efforts (“Queen of Swords”), Menzel was a bundle of majestic vocal swoops throughout.

Though some of the audience appeared to be unfamiliar with – or apathetic about – her music and her efforts to promote engagement, Menzel and her band clearly had a blast.

She dropped in a slinky recast of Modern English’s 1982 hit, “I Melt With You,” noting that it used to remind her of her junior high boyfriend, but now “make me think of my husband” and, following a thundering drum introduction, unleashed the still-enjoyable “Let It Go.”

She endeared herself to the “Rent”-heads in the crowd with a funky run through “Over the Moon,” a gut-busting “Take Me or Leave Me” – which featured a vocal battle royale between Menzel and her backup singer – and the warm embrace of “No Day But Today.”

While fans of Menzel’s bottomless vocal power no doubt adored her set-closing “Defying Gravity,” it was actually the penultimate performance – an a capella read of the most tender song from the “Wicked’ canon, “For Good,” that inspired chills.

Menzel, obviously, can belt. But unlike many of her peers, she’s possesses the skill to understand when less is so much more powerful.

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