If you were one of the few dozen stagehands, producers, technicians or reporters who just happened to be working in Radio City Music Hall on Saturday night (September 12), well, then you must be feeling pretty good right now. Because you were lucky enough to witness a very special, very off-the-cuff concert by Green Day.

In part to break the monotony that comes with Video Music Awards soundchecks - [article id="1621348"]a process that could best be described as repetitive[/article] -- and partially as a kind gesture to the men and women who have been working day and night to get Radio City ready for the big show on Sunday, Green Day decided to let loose onstage,, working their way through a high-energy set of hits both old and new.

And yes, it was pretty amazing.

"For us to get used to a stage, we just have to play for a long time ... and there were a lot of people, and it seemed like they were just tired, they'd been working here all day, getting the production together," Billie Joe Armstrong told MTV News after rehearsals. "So we ran through 'East Jesus Nowhere' a couple times and then we were like, 'The hell with it, let's just jam.' So we played 'Longview,' 'Murder City,' 'Holiday,' 'American Idiot,' 'Know Your Enemy.' We just kept going, and I got up dancing, so it was pretty cool."

At set's end, the assembled crowd stood and cheered, clearly grateful for -- and amazed by -- what they had just witnessed. And Armstrong seemed equally energized, grabbing the mic stand and screaming, "Now there's a vibe in here! It feels like a Green Day concert!"

Of course, a bit later, he tried to downplay the whole thing. Green Day were here to rehearse, he reasoned, so that's what they did. But that was just modesty; this kind of thing rarely happens at rehearsals, where bands usually look like there are about a million places they'd rather be. Not Saturday, though.

"That's what we're supposed to do, you know? Play," Armstrong said. "We've had a lot of happy accidents. I think most of the stuff we do onstage was probably due to too much alcohol and then something happens. So we end up with these three-hour sets of just, like, shooting a toilet-paper gun at people or something. [We do it] just to have fun. It just works that way for us."

Watch the 2009 MTV Video Music Awards Preshow this Sunday, September 13, at 8 p.m. ET, followed by the big event, live at 9 p.m. Check out our interactive map of New York to see how the city is celebrating the VMAs all week long, and stay tuned for party coverage, concert reports, behind-the-scenes updates and more.