Prior to last night's sold-out performance at The Riverside, I expected to see The Swell Season play the songs from the film "Once" and be done with it.

Instead, romantically-linked musicians and stars of "Once," Glen Hansard and Markéta Irglová, delivered a three-hour show -- along with their band -- that waivered between an explosion of raw emotion and an Irish hootenanny.

Opening act Damien Dempsey -- reportedly found by Hansard busking on the back streets of Dublin -- promised The Swell Season would "knock your socks off," and if I had been wearing any, they would have unraveled into a heap of synthetic, argyle fibers. Maybe even started on fire.

Yes, it was that amazing.

Hansard opened the show, without a mic, singing the beautiful "Say It To Me Now" from the "Once" soundtrack, and then introduced the Czech singer, songwriter and pianist, Irglová.

Both appeared almost identical to the characters they played in the film. Hansard, who wore jeans and a work shirt with a blazer over it, maintained an infectious smile for most of the show, whereas Irglová was gentle and more stoic, dressed in a long red skirt and black top.

She did, however, absolutely beam when Dempsey told a story during the encore about the first time he saw Hansard perform in Dublin and how his singing made the hair on the back of his neck stand up.

Irglová, 20, and Hansard, 38, fell in love during the making of "Once," which adds a deeply intense dimension to the film and the music. The couple, who started The Swell Season the year before the film came out, wrote all but one song on the soundtrack.

Earlier this year, they won an Academy Award for the soundtrack's big hit, "Falling Slowly."

Hansard -- who is every bit as much a storyteller as he is a musician -- said the unexpected popularity of "Falling Slowly" made him feel like a kid who kicks a ball, hoping to make it past the garden, but instead, slams it over the garden, over the fence, over a river, over a town and into outer space, leaving the boy completely amazed, but also wishing he could get his ball back.

Hansard went on to say that he received an e-mail from the Whitefish Bay Middle School choir saying they had performed "Falling Slowly," so he invited the group to join him on stage.

After joking that the choir -- comprising suburban middle schoolers -- looked like the cast of "Freaks and Geeks," they went on to belt out a rich version of "Falling Slowly," followed by a funny-but-unrehearsed version of The Pixies' "Gigantic."

Hansard also fronts the Irish folk rock band The Frames. "Once" director John Carney was the former bassist.

Hansard's enthusiasm and passion fueled the entire concert. His delivery of "When Your Mind's Made Up" was even more powerful and emotionally intense last night than it was in the movie. Although the show didn't end until 11:20 p.m. -- after a five-song encore that included an audience request for "Broken Hearted Hoover Fixer Song" -- it was apparent that he could have gigged all night.

Perhaps the most refreshing aspect of The Swell Season is a complete void of irony and sarcasm. Sure, at times they teeter on the corny, but Hansard's and Irglová's sincerity is a major factor in the popularity of their music.