It was the unannounced performers on an already star-studded bill at the SOB's 30th Anniversary show on Wednesday night (March 14) that became the talk of the town. The concert, held during SXSW, drew in fans and industry muscle with a line up that included Slaughterhouse, 2 Chainz, Machine Gun Kelly and Travis Porter, to help celebrate 30 years of the historic New York City live music venue. But it was when 2 Chainz brought out Def Jam labelmates Kanye West and Big Sean that the crowd hit a fever pitch.

After acts including Anthem, Elle Varner, The Airplane Boys and Miguel hit the stage, Travis Porter turned up the energy by performing a string of their club bangers. Kicking off their set with “You Don't Know Bout It,” the trio then decided to bring attendees to the strip club and “Make It Rain.” The Atlanta natives brought their time to a close with their two most recent Billboard charting singles, the Tyga-assisted “Ayy Ladies” and the infectious “Bring It Back.”

Following TP was an artist with whom they've collaborated a handful of times, as Machine Gun Kelly brought his rowdy approach to the outdoor venue. The 2012 XXL Freshman ran through joints from both his Lace Up and Rage Pack mixtapes, including “Chip Off The Block” and “Warning Shot.” The Cleveland native also treated fans to “Invinsible,” which has been included in Beats By Dre commericals and selected as the theme song to the upcoming WrestleMania XXVIII in Miami. Kells, who just this week released the “Wild Boy (Remix)” alongside 2 Chainz, Meek Mill, French Montana, Yo Gotti, Mystikal, and Steve-O, rocked out to the original—even bringing a pint-sized fan on stage to party, before tossing him into a sea of extended arms to crowd surf.

MGK headed off stage to tag in “Wild Boy (Remix)” cohort 2 Chainz, and the Atlanta representer made his presence known. After confidently walking out to—but not rapping—his T.R.U. Realigion lead in cut “Got One,” Tity navigated the crowd through some of the release's standouts like “Turn Up” and “Riot.” Shortly after offering his verse to “SupaFreak,” from Young Jeezy's TM:103 Hustlerz Ambition album, the long-haired rhymer flowed into another joint for the ladies, “K.O.” Halfway through the song, 2 Chainz brought out Big Sean, who then performed his verse. Sean got a little bit of stage time on his own, as he moved the crowd to “A$$ (Dance).” Then, just as 2 Chainz was getting ready to get off stage, he revealed that he brought another friend along, and from the bustle of backstage, Kanye West emerged. As cameraphones illuminated the night sky, the DJ threw on “Marvin & Chardonnay,” and the two G.O.O.D. Music members traded verses.

Yeezy then briefly spit some of his “Can't Tell Me Nothin',” before the squad posed for pictures for photographers and the crowd and scurried off stage.

Such unexpected excitement would be a tough scene for any artist to follow. Lucky for Slaughterhouse, there were four rappers, rather than one, to continue to carry the momentum. The Shady Records rappers did just that, bringing the evening to a fitting conclusion with an array from their arsenal, ranging from their 2009 album's opener “Sound Off” to their BET Awards Cipher to “Hammer Dance,” the new single from their upcoming album welcome to: Our House, due out in May. The four-headed monster had some guests of their own, as well, as MC Hammer and New York Giants wide receiver Victor Cruz posted on stage and rapped along.

Earlier in the evening, a video commemorating the historic anniversary for SOB's recalled some of the venue's lure and great moments. —Adam Fleischer