SANTA ANA, Calif. - Brian Decal, 24, drove out from the San Fernando Valley, arriving at 8:30 a.m. for a gig that wouldn’t start for another 12 hours. He wasn’t even sure he’d get in.

A little while before show time, “The security guy said, ‘Give us your names. We’re not promising anything but we’ll see if we can get you in.’” He was one of the last to gain entrance. Roland Valencia, 18, of Anaheim, Calif. - he was the very last.

“I feel like the luckiest guy in the world right now,” he said afterward.

Marshall Rhodes, 18, of Los Alamitos - he got in line at 6 a.m. for what would be his first ... er, second show. “I went to an ‘N Sync concert with my sister,” he confessed later, his shirt sweat-soaked and sticking to him. “But that doesn’t count.” If he’d said it any louder, in fact, he might’ve gotten punched.

Joey Lohran, 20, of Whittier, along with his sister Kristie, 22, and their friend Bianca Reyna, 18, of La Mirada - they stayed up all night, pulling into the Anaheim parking lot at 4 a.m. “And there was already a line all the way around the block!” Joey said, recalling the throngs of people who had camped out in sleeping bags.

“But the Offspring playing a free show at Chain Reaction? Doesn’t get any better or smaller than that!”

Actually, the long-running punk band from Huntington Beach has turned up in a tinier O.C. venue - but that was back in December ‘95, when the Offspring used Linda’s Doll Hut (capacity 49) for a secret warm-up gig before a benefit performance at the Hollywood Palladium. The group had just begun to break big on the back of its aptly-named, now-seminal 1994 album “Smash,” still the biggest-selling indie release in history. At the time, before that disc catapulted them to stardom, it hadn’t been uncommon to find the quartet bashing out new tunes at the Doll Hut.

But in the 14 years since the Offspring became a multiplatinum modern-rock staple, the band - frontman Dexter Holland, guitarist Kevin “Noodles” Wasserman, bassist Greg Kriesel and new drummer Pete Parada – hadn’t stepped into a shoebox in its home county quite as small as Chain Reaction. The place is so cramped - capacity 250, though it sure felt like there were a lot more people stuffed in there Sunday night - that whenever Noodles would excitedly pogo, it often looked as though he would put his head through the roof.

What brought the band and scores of rabid fans to this all-ages hole-in-the-wall? MySpace and its ongoing series of not-so-secret shows. This one was announced in a bulletin from the social networking site Friday morning, though most attendees I talked to heard about it on radio.

And they had waited so long for it to kick off that by the time the Offspring finally hit the stage, just before 9 p.m., the joint was like a powder keg about to go off. The crush of kids pressing toward the stage looked suffocating.

“You guys are (bleepin’) pumped up!” Holland noted after the group ripped through its first two songs, “All I Want” (during which he was completely drowned out by chanting devotees) and its first big hit, “Come Out and Play (Keep ‘Em Separated).” “Pumped up” is a gross understatement. One giant mosh pit never seemed to stop swirling, even during the now kinda-hokey novelty “Pretty Fly (For a White Guy).” Tossed water bottles splashed overhead virtually every other song. I hung to the rear – and watched one dripping, dehydrated kid after another pull away for a breather.

Undoubtedly they got more than they anticipated, as the Offspring all but ignored its new album, “Rise and Fall, Rage and Grace,” cherry-picking three of its strongest cuts (including “Hammerhead” and “Half-Truism”) in favor of roaring through old favorites and long-neglected tunes like “Burn It Up” and “Mota.” That last one, repeatedly shouted for by the crowd, required them to take an impromptu break, to step offstage and remember how to play it.

In true punk fashion, nothing was pitch-perfect (Holland surely couldn’t have heard himself very well) and everything seemed to fly by at breakneck speed; I’ve never encountered a more turbulent “Bad Habit,” while “Staring at the Sun” and “Genocide” often threatened to race right off their railings. Not surprisingly, the crowd, which hollered along to new songs with the same enthusiasm as it had for old ones, matched the band in intensity, egging it on to a more explosive performance.

By night’s end, you couldn’t escape the sweat – and some couldn’t find shelter from the insanity. On my way out I ran into Matt Hammon, 23, of San Clemente, leaning against a wall, a deep gash in his forehead, blood on his chin, arms and hands. Someone had kicked him during the last song, and he did a face plant.

Refusing to go to an emergency room, Hammon said he didn’t mind the pain one bit. “I’ve been in crazier pits than that,” he said, still conscious. “It happens. You gotta expect it to happen. If you get hurt, it’s part of life. It’s a learning experience, and it’s fun.”