PHILADELPHIA -- Before Fall Out Boy would prove itself a tastemaker in pop's emo-punk fascination more than a decade ago -- the same surge that promoted Paramore, Panic! At the Disco and New Jersey's own My Chemical Romance from club circuits to headlining arena tours -- the Illinois four-piece was no more than a cushy side project for members of more assailing acts.

Patrick Stump, Pete Wentz, Joe Trohman and Andy Hurley were all players in Chicago's underground hardcore punk scene, where bands were measured by the size of their mosh pits and their resolute ferocity on stage. It was cool to look like you hated what you were doing, as long as your group's rhythmic breakdowns were heavy enough to set off the fire alarms. No smiles, no problem.

Flash forward to 2017 and Fall Out Boy is four years -- and two No. 1 albums -- deep into its spectacular second act, as a reimagined, pop-first rock band that now relies on triumphant synth and drum machines, as opposed to a catchy guitar hook, to fuel anthems that seem to grow grander with every release. A new album called "Mania" drops Jan. 19.

Fifteen years later, a Fall Out Boy concert remains an arena event overrun by teens: some swiped from the trendier pop audience, others still rocking their in skinny jeans and complimenting each other on the blue streaks colored into their hair. Few bands from pop-punk's turn-of-century heyday have made so seamless a transition from Warped Tour darlings to hit radio mainstays.

Yet in Philadelphia Sunday night, something was off. It felt as though after all this time, that midwestern hardcore solemnity still exists within the band, as if to say "don't have too much fun out there, you sell-outs."

More simply put: for all the pyrotechnics, floating stages and confetti a Fall Out Boy arena show promises, the band itself just isn't very much fun to watch. The buoyancy that continues to lift the live shows of pop-punk influencers blink-182 and New Found Glory has somehow been lost on these guys.

The singer Stump, dressed for the night's pouring rain in a hoodie, jacket and baseball cap, occasionally loosened and shuffled his feet inside the Wells Fargo Center bowl. He was stronger still when he relinquished the rhythm guitar duties that kept him pinned to his mic stand most of the night, and danced around the rectangular stage for the propulsive jam "This Ain't a Scene, It's an Arms Race," or plinked a baby grand piano for the sweeping 2013 ballad "Save Rock and Roll" and its sure-handed vocal part (Elton John duets on the studio recording). Stump can belt with command when called upon, and maintains a rich, low register, though some high notes rang out as shrill.

The rest of the band spent the 90-minute set robotically trotting down the stage's runway that split the arena in two, strumming and drumming with minds elsewhere. Lead guitarist Trohman possessed all the charisma of a Walgreens cashier and the drummer Hurley only lit up when given a mid-set drum solo, taken on a floating B stage, which showcased sincere skill but also revealed just how wasted his ability is on most of the band's rhythmically simple hits.

To that end, I'm not sure I've ever seen a bassist with less challenging pieces than the group's figurehead Wentz, who picked his eighth-note riffs easily as he waltzed around the stage. If you have a child who wants to learn bass guitar, download him or her some Fall Out Boy tabs.

Sonically, this was a worthy show; the old pop-punk staples like "Sugar, We're Goin Down" and early favorite "Grand Theft Autumn/Where Is Your Boy," still hit hard, and the new "Mania" single "The Last of the Real Ones" marks another tightly written tune. And kudos to the fan-led effort that placed a small, purple paper filter on each seat in the arena, which thousands placed over their smartphone flashlights and illuminated the venue in violet as Stump played the newbie "Young and Menace." I hadn't seen that trick at a show before.

But I have witnessed plenty of bands who don't appear comfortable in their own skin, and a decade from now or later, when Fall Out Boy is nominated for the Rock and Roll Hall of Fame -- maybe that sounds crazy now, but it's coming -- I'll remember them as the band who just couldn't relax.

Fall Out Boy's set list

Oct. 29, 2017 -- Wells Fargo Center, Philadelphia

"The Phoenix"

"Irresistible"

"Hum Hallelujah"

"Sugar, We're Goin Down"

"Alone Together"

"Immortals"

"American Beauty/American Psycho"

"Centuries"

"Save Rock and Roll"

"The Last of the Real Ones"

"Young and Menace" (Patrick Solo Piano)

B-Stage:

Drum Solo

"Dance, Dance"

"Expensive Mistakes"

"Thnks fr th Mmrs"

Intermission (Video interlude)

"I Don't Care"

"This Ain't a Scene, It's an Arms Race"

"Grand Theft Autumn/Where Is Your Boy"

"Champion"

Encore:

"Uma Thurman"

"My Songs Know What You Did in the Dark (Light Em Up)"

"Saturday"

Bobby Olivier may be reached at bolivier@njadvancemedia.com. Follow him on Twitter @BobbyOlivier. Find NJ.com on Facebook.