The 18-year-old singer was nearing the end of a private show when the power for most of the stage instruments suddenly went out. The partial blackout lasted more than 40 minutes.
Bieber still managed to finish his show without most of the stage instruments. He got help from fans singing along with him.
"He walks out, he literally quiets the crowd, and he says, `I'm sorry the power is out. . (But) you guys have always had my back. I'm going to sing `Boyfriend' and you're going to sing it back to me,'" said his manager, Scooter Braun.
"What it turned into was an Apollo moment, like one of those impromptu things," said Nina Flowers, the Apollo's rep.
The singing sensation blamed the power outage on all the "hot girls in the audience."
The concert was part of a series of promotional appearances to push his album "Believe," which was released on Tuesday.
The cause of the power outage is unknown at this time.
The Associated Press contributed to this report.