NEW YORK — As a musician, Pete Wentz is a really killer businessman.

He's got a successful label (Decaydance, home of Panic! at the Disco), a clothing line (Clandestine Industries) and an online community (FriendsOrEnemies.com, a sort of bizarre Friendster where users can vent their hatred toward their fellow man), all borne from deceptively brilliant viral marketing campaigns, each sporting their own glossy Web sites. And his band, Fall Out Boy, has ridden a wave of hardcore touring and message-board postings to multiplatinum success. Adding to it all, Wentz frequently pens lengthy, heart-on-his-sleeve journal entries on FOB's site. If there's a poster boy for the rise of the Internet generation, it's probably him.

So it made sense that when Fall Out Boy finally chose to play a secret show, they announced it in the form of a quiet little listing on TicketWeb.com, under the "Rushmore"-approved name of Saved Latin. Then they just sat back and let the buzz grow.

Tickets sold out in less than 48 hours, and by the time Fall Out took the tiny stage at the Knitting Factory on Friday, the excitement in the crowd was palpable (and the preteen screeches ear-splitting). Each and every raccoon-eyed girl and angular-haired guy in the audience believed that they were part of something underground, something that the cheerleaders and jocks had no idea was happening. Judging by the number of cell phones held aloft, the goal was to make those cheerleaders and jocks very jealous at school on Monday (or at least score some sweet pics for their blogs).

And FOB, perhaps sensing that vibe, delivering a set full of "I was there when ..." moments. They led off with a pair of tracks from 2003's Take This to Your Grave ("Tell That Mick He Just Made My List of Things to Do Today" — hey, another "Rushmore" reference — and "Dead on Arrival"), and then dug deeper (all the way back to 2002), ripping through "Honorable Mention" from their debut, Fall Out Boy's Evening Out With Your Girl.

Of course, they also played the hits. Just like he did at FOB's pre-Grammys show in Los Angeles last month (see "Fall Out Boy Finally Become Rock Stars, Thanks To The Ghost Of Big-Hairs Past"), Wentz introduced "Sugar, We're Goin Down" as "the reason we don't play small venues anymore," and they were joined onstage by My Chemical Romance bassist Mikey Way for "Dance, Dance."

Through it all, the band was its normal, slightly silly self. Frontman Patrick Stump shimmied his hips and smirked his way through the set. Guitarist Joe Trohman maintained his status as the goofiest guy in rock, making wide-eyed monkey faces and karate kicking his amp. Drummer Andy Hurley was his usual metronomic, tattooed self. And Wentz did what he does best; deliver sermons to the masses. His between-song-banter ran the gamut from cringe-inducing ("This song is about wanting to burn the suburbs down") to head-scratching ("I'm sorry I'm a little down, I just threw up an hour ago"), but this being his target audience, he managed to hit his marks.

He chided an overly aggressive meathead in the crowd by telling him that "fighting at a Fall Out Boy show is pretty dumb ... but not as dumb as fighting on LiveJournal" (a reference to an ongoing beef between himself and Chicago blogger "AskHeyChris"), and gave the audience the inside scoop on Fall Out's upcoming video for "A Little Less Sixteen Candles, A Little More 'Touch Me' " (see "Fall Out Boy Promise An 'Event' Video For 'Sixteen Candles' ") provided they didn't go home and blog about it (wink, wink). And near the end of the set, he whipped out a digital camera, urging the crowd to throw up the Roc-A-Fella sign so he could snap a photo for his pal Jay-Z (like Jigga said, "I'm not a businessman, I'm a business, man!").

About the only un-slick, unscripted moment came at set's end, as Wentz climbed to the Knitting Factory's upper balcony and prepared to take a plunge into the waiting arms of the crowd. The only problem was the crowd didn't quite seem to know what to do, and as Wentz leapt, fans only sort of caught him, and he went "down, down" (hard) to the concrete floor. He ended up being OK (though he missed the afterparty), and as bouncers hoisted him back onstage, a humble grin creased his lips. It was almost like he couldn't wait to read what the message boards were gonna say about it. And he was probably already formulating his response.

For more sights and stories from concerts around the country, check out MTV News Tour Reports.