The Impossibles faced a two-part challenge Saturday night at the M-Shop. They already knew about the first part: fans of the band always want to hear songs from The Impossibles’ early days of ska.

The second part, however, probably came as a surprise to the Austin, Texas-bred band: opener River City High made the crowd as much a part of the show as the band itself, putting The Impossibles in position to be upstaged.

However, Rory Phillips, guitar and vocals, Gabe Hascall, vocals and guitar, Craig Tweedy, bass, and Kemble Walters, drums, played with unparalleled passion, ripping through a relatively short and fast-paced set that featured only two retooled ska songs.

“Don’t you know that’s the reason we got a new drummer?” Phillips said in response to numerous crowd requests for old Impossibles tunes. “So we have a reason not to play certain songs.”

It didn’t matter that the band has pretty much abandoned its past music for a complete sound reinvention; the new material, including songs from 2000’s “Recover” and this year’s “Four Song Brick Bomb,” stood on its own during The Impossibles’ performance.

Fans of the band’s ska catalog had no reason to be disappointed by the lack of skank-inducing songs.

“Disintegration” (the best album, ever), Phillips’ tribute to his days as a devoted and depressed fifth grade Cure fan, proved that the band’s move to an indie-pop sound was not a mistake.

The song’s Weezer-esque harmonies and well-placed tempo changes furthered the frenzy of both bass player Tweedy and the crowd in what seemed more a musical conversation than a concert.

Crowd and band fed off each other; members of The Impossibles confronted the fans nearest the stage, getting face to face and pulling rock star poses.

Lacking vocal responsibilities, Tweedy was able to further express his enthusiasm for rocking Iowa, a place the band had heard was “cool.” He was in constant motion, either falling to his knees in sync with the music or running around the stage.

Smiles and bright eyes were obvious on the faces of the members of The Impossibles as they played, something that lifted their performance slightly above River City High’s phenomenal set.

The pop punk-tinged melodic rock quartet showed that it is making a bid for Warped Tour stardom with a tight, energetic set that surprised a crowd expecting The Impossibles to dominate the night.

River City High started the fist-pumping and flowing moshing that characterized The Impossibles’ performance. They capped a solid show with a tongue-in-cheek version of “The Boys Are Back in Town” that inspired metal signs galore.

The Impossibles’ labelmates Recover played well but left the crowd confused by its melodic hardcore contrast; one vocalist screamed while the other sang melodically, making for a powerful combination.