Stuart Ward as Guy and Dani de Waal as Girl in “Once,” the musical adapted from a 2007 movie about a Dublin busker and the woman with whom he strikes up a collaboration. (Joan Marcus)

In the half-hour before the musical “Once” begins, you can hit the cash bar on the Kennedy Center’s Eisenhower Theater stage and hang out with musicians serving up foot-stomping songs. The performers in this 2012 Tony-winning Broadway show play guitars, mandolins and fiddles on the Dublin pub set. They romp around and sing up a storm. It’s a party.

There is more high-spirited energy in this pre-show fun than in the entire understated 85-minute movie that inspired this unlikely stage hit. The 2007 film was a quiet treasure about a lovelorn Irish street musician (known as Guy) and an immigrant Czech woman (called Girl) who strike up a friendship. Washington Post film critic Ann Hornaday called the picture a “bona fide alt-Celtic indie busker musical.”

If you revere the film, you may resist the added comic padding “Once” now has. The normally tough-minded Irish playwright Enda Walsh, subject of an ambitious 2011 festival at Washington’s Studio Theatre, has whipped up adorable dialogue for the semi-flaky characters populating this pub. The musical is frosted with punch lines and cliches that never would have cut it in the austere movie, which was largely shot on Dublin’s streets.

That’s nothing, of course, next to the hyper-self-aware laugh riot “Book of Mormon” from the creators of “South Park,” running next door in the Opera House. If you’re a theater buff, you’ll understand how calm, sensitive and genuinely charming this staged “Once” has turned out to be, winsome new jokes and all. And the core of the picture translates beautifully — the gorgeous, savage way Guy hammers his acoustic guitar, crooning and bellowing desperate love songs that seem written in blood.

The adaptation is by John Tiffany and Steven Hoggett, the director and choreographer who brought you the riveting military drama “Black Watch.” (That came to the Shakespeare Theatre Company twice, by way of the National Theatre of Scotland.) They’ve swapped the introspective realism of John Carney’s movie for a high theatricality: Most of the 13 actors stay on stage the entire time, playing all the instruments and whisking furniture in place to change scenes.

Stuart Ward and Dani de Waal. (Joan Marcus)

As a concept, that’s fine, and designer Bob Crowley’s wide barroom rimmed with weathered mirrors leaves ample space for all the make-believe. But what elevates the performance is the treatment of the songs (including the Oscar-winning ballad “Falling Slowly”) written by Glen Hansard and Marketa Irglova, who on screen played Guy and Girl falling in love over their music. The signature is Guy’s anguished, soulful troubadour solos, which Stuart Ward delivers with authority and enough ferocity that his first song (“Leave”) deliberately wrecks that opening feel-good vibe among the revelers in the pub.

Dani de Waal is a stabilizing force as Girl, playing a little Mendelssohn on piano and quickly anchoring Ward’s slightly over-brooding Guy in tender duets. The way the story goes, this musical collaboration widens and includes a misfit pickup band they recruit for a recording session. (The love story is complicated: Guy and Girl are both sort of otherwise attached.)

The thrill of the show, though, is that the music is always in front of us, and always in splendid shape. The actor-musicians are proficient with their instruments, and the arrangements are powerful and exquisite — four or five guitars at once with accordion, fiddles, ukulele, percussion and, soaring angelically, a voice, or maybe 10. The performers’ touch runs from aching delicacy in an a capella chorus to ecstatic frenzy as the group records Guy’s bitter anthem “When Your Mind’s Made Up.”

The movie tells the story better; the picture allowed nothing extra, and its raw, tight-lipped sincerity is sterling. Yet as Broadway swipes for every movie title it can get, the musical version doesn’t smell like a rip-off, even if the Girl is now overwritten as a guardian angel and the supporting characters (a droll and burly shop owner, a bank manager who longs to be a musician) could start a sit-com. Hoggett’s restrained musical staging has a ritual quality illustrating how the songs catapult these everyday Dubliners into an extraordinary realm, and the bittersweet romantic tension of those songs makes it from screen to stage intact. This small show easily does what bigger shows work so hard to do: It lifts you up.

Once, music and lyrics by Glen Hansard and Marketa Irglova, book by Enda Walsh. Directed by John Tiffany. Music supervisor and orchestrations, Martin Lowe. Costumes, Bob Crowley; lights, Natasha Katz; sound design, Clive Goodwin. With Sarah McKinley Austin, Matt DeAngelis, John Steven Gardner, Evan Harrington, Ryan Link, Benjamin Magnuson, Alex Nee, Erica Spyres, Tina Stafford, Erica Swindell, and Scott Waara. About two hours and 20 minutes. Through Aug. 16 at the Kennedy Center Eisenhower Theater. Tickets $65-$160. Call 202-467-4600 or visit www.kennedy-center.org.