The Swell Season performed several concerts in one on Wednesday at the Michigan Theater, treating a very nearly sold-out audience to a delightful evening of gorgeous harmonies, inventive arrangements and perhaps a little more rock ’n’ roll energy than most expected.

The band — the expanded, real-life version of the singers at the center of the movie “Once” — assumed multiple identities, all of which revolved around the duo of Glen Hansard and Markéta Irglová, who played the leads in the film, and wrote and performed the bulk of the Swell Season’s catalog.

The two entered together on Wednesday and sat on the stage to perform a guitar-and-keyboard duet on “Fallen From the Sky,” setting the scene for the vocal interplay that would mark the rest of the show.

But unlike the pair’s performances in the movie, the Swell Season boasts Hansard’s longtime bandmates, The Frames, whose addition following the opening tune kicked the show into a folk-rock frenzy that, although it ebbed and flowed as Hansard and Irglová took solo turns, provided the evening’s most satisfying moments.

Hansard was clearly the star of the show. A natural frontman with a rich voice that can channel everyone from Cat Stevens to his Irish countryman Van Morrison, he charmed the audience with those talents, as well as a gift of gab alternating from poignant to funny.

A short solo set in the middle of the concert found him onstage alone, coaxing surprisingly serviceable backing vocals out of the audience and delivering a blistering version of Morrison’s “Astral Weeks.”

Glen Hansard of the Swell Season performing "Astral Weeks" live in Oakland last month:

Markéta Irglová was less convincing during her turns in the spotlight. While a gifted singer, her voice is better suited to the harmonies she provided to most of the Swell Season’s tunes, and she appeared nearly stricken when called upon to perform on guitar instead of behind the piano. And Hansard was such a dominant frontman that his persona perhaps cast an unfair shadow over Irglová’s solo moments.

Of course, the unsung heroes of the evening were the Frames, a band that’s popular in its native Ireland but now getting its first tastes of widespread exposure in backing the Swell Season. The four-piece combo rocked hard behind Hansard and offered just the right counterpoint in support of Irglová.

And those harmonies. Hansard and Irglová are two singers who are meant to sing together. Sure, the pair’s songs can be a little cloying at times — most seem to revolve around the general notion of setting a lover free — but the singers find something interesting enough vocally in each one to hold the listener’s interest.

After a short break, just Hansard and Irglová returned to the stage to duet around the piano on “Falling Slowly,” the Academy Award-winning song from “Once,” bringing the audience to its feet and inspiring more than a few sing-along moments.

The Swell Season performing "Falling Slowly" live in Seattle in October:

By the time the song’s final chord wafted through the theater, many in the audience, having heard what they came for, were heading for the door. A shame, as the band had a few more tricks up its sleeve, ending its set with the powerful “High Horses” and the Frames’ lovely “Red Chord.”

It was a fittingly beautiful end to an equally lovely evening of music.

Will Stewart is a free-lance writer for AnnArbor.com.