AUSTIN, TX - MARCH 15: Musician Billie Joe Armstrong of Green Day and a fan perform during the 2013 SXSW Music, Film + Intera
Michael Buckner

When Green Day kicked off their first-ever SXSW set, everyone in attendance already felt lucky to be there. Even those with SXSW badges had to enter a ticket lottery to win entrance to the highly anticipated concert, which was their first major show since Billie Joe Armstrong's rehab stint last year. So anyone at Austin's Moody Theater on Friday night was just pumped to be there in the first place.

Green Day's intimate gig and more highlight our daily SXSW photo gallery.

But for one incredibly lucky fan, the SXSW highlight became a once-in-a-lifetime victory when Armstrong brought her onstage to trade vocals with him. And for the rest of the audience, it was impossible to be jealous while watching her go from flabbergast to utterly ecstatic.

After catching hold of her runaway emotions—you could read the varying shades of shock play across her dazed face—the fortunate fan joined Armstrong onstage and even earned a full-on kiss from the frontman. And in true punk fashion, she made her exit by launching into the audience and crowd surfing her way back into the masses.

Green Day and a fan perform at Moody Theatre on March 15, 2013 during the SXSW Music Conference.
Joe Lynch for Fuse

Later in the show, Armstrong brought another fan onstage—this time an adorably floppy-haired dude—to take over the third verse of "Longview." But that kid was ready for his chance to front one of the biggest rock bands in the world.

Forgoing the expected ohmygoshthisisreallyhappening state of shock, this teenage kid prowled across the stage like Iggy Pop delivered the Dookie track as if it were his own. You gotta hand it to him—not too many people have had the chance (or the courage) to turn Green Day into a live karaoke outfit.

As for the band itself, Green Day clearly relished being back onstage with renewed energy and purpose. They were tight on classic tracks like "Burnout" and "Welcome to Paradise," appropriately anthemic on "Boulevard of Broken Dreams" and charmingly loose on a medley of covers that included "Stand By Me," "Sweet Child O Mine" and even "Hey Jude."

The only sign of Armstrong's stumble last year came via a willing reference to his rehab stint. After an issue with his mic, Armstrong laughed and quipped, "I wasn't even on drugs."

It was a welcome reminder that despite their long-running world domination, Green Day haven't lost the casual authenticity they've sported since forming back in 1987. Which, coincidentally, was the same year SXSW started. And given this was their first go-around at the Austin music fest, it was high-time these two cultural touchstones finally crossed paths.