During Monday's auditions in Greensboro, N.C., Spears stormed off the set as a man, dressed partially as a woman, rocked through one of her hits, "(You Drive Me) Crazy."
Spears, 30, looked stunned throughout the performance, as fellow judge L.A. Reid patted her on the back. Judges Demi Lovato and Simon Cowell also couldn't contain their reactions, as they covered their faces with their hands.
While Reid and Lovato followed the pop star off the set, Cowell stayed behind. "I don't think she quite understood your tribute," he told the singer.
"I had to fight real hard to get here," the tearful singer told the judges, adding that he was recently on welfare and nearly missed his X Factor call because he couldn't afford his phone bill.
"I really respect the tribute," Spears said when she returned to the judges' table. "It was really nice."