Photo: Ach/WireImage for ActiVision

Jay-Z was an hour into a set that was only supposed to be 45 minutes last night at New York’s Gramercy Theatre, ripping through a fierce, nimble version of “You, Me, Him and Her” when the venue’s fire alarm went off. At first the persistent buzz seemed like it could have been coming from Jay’s massive live band, but the look of pure disgust on the Brooklyn rapper’s face revealed otherwise. Undeterred, he returned to the stage five minutes later, towel around neck, as a handful of New York City firemen watched baffled from the back of the floor with oxygen tanks strapped to their backs.

It was a surreal moment at an unbelievable show — a tiny free performance thrown by MySpace and DJ Hero the week of The Blueprint 3’s (early) release and two days before Jay is due to take on a much larger venue: Madison Square Garden, where he’ll play a 9/11 benefit Friday night. After an impressive demo of the game, which comes out October 27th (more on DJ Hero here), the hook from “Run This Town” began to play and Jay-Z took the stage, bathed in purple light. He ran through the first two BP3 singles and paused after “U Don’t Know” to chastise members of the crowd who hadn’t yet rose to their feet: “All you homeboys sitting on the steps, you’re fucking my whole vibe up and shit.” If his playful jab didn’t do the trick, a raucous “99 Problems” did as Jay stalked the stage in shades and a black T-shirt with three red stripes on the arm, an homage to his BP3 album cover that seemed like it could have been a fashion tip from pal Chris Martin.

After the new album’s “Venus Vs. Mars” and “Hate,” Jay peeled off verse after verse from some of his biggest hits: “Public Service Announcement,” “Heart of the City,” “Izzo (H.O.V.A.)” (as his band rocked the Jackson 5’s “I Want You Back”), “I Just Wanna Love You (Give It To Me),” “Dirt Off Your Shoulder,” “Show Me What You Got.” “They told me to do 45 minutes, but I’m gonna to an hour 15 and shit,” he announced and answered the crowd’s chants of “Brooklyn!” with a mind-blowing rendition of “Brooklyn (Go Hard)” that didn’t even miss its Santigold cameo as Jay called for his drummer to drop out so he could vibe along to the keyboard line.

When Jay returned from the alarm scare, he was fired up to close out the set hard, demanding the crowd sing the “Annie” hook of “Hard Knock Life (Ghetto Anthem)” (the effect was quite odd). Then he thanked the crowd “for all the love — I appreciate every single person in the building” and tossed off his shades for the only appropriate closer: “Encore.”

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