Like the first time, it was well-received.
"I'm gonna give you an A-plus for that one dude, A for Adam!" gushed judge Randy Jackson.
Allen followed Lambert's performance with "Ain't No Sunshine." The judges' panel loved the rendition, which featured Allen on the piano.
"When your name was announced last week, I wasn't sure that America had made the right choice," he said. "I absolutely take all that back now after that performance."
With that, Cowell declared Allen the Round One winner.
The tide quickly turned - Lambert replaced his gloomy overcoat with a suit and tie for the second round of the sing-off and performed the Sam Cooke classic "A Change Is Gonna Come." The effect was soulful and over-the-top, flaunting Lambert's vocal range and theatrical delivery.
"That was the best I've ever heard you sing - ever!" crowed Paula Abdul.
Next up, Allen turned to trusty guitar for the Marvin Gaye tune "What's Going On."
Cowell disliked his interpretation, saying it sounded like "three friends in their bedroom strumming along to Marvin Gaye. ... I thought it was too laid-back for a night like this."
Round Two goes to Lambert, "a million percent," said Cowell, the de facto round-caller - though America's votes will really decide the outcome.
Lambert and Allen are slated to perform three songs a piece: a favorite performance from this past season; a tune selected by "Idol" creator Simon Fuller and a song co-written by Kara DioGuardi, the show's fourth judge.
NEW YORK AND TRI-STATE AREA NEWS
SEND TIP OR PHOTO || REPORT TYPO || GET WIDGET
EYEWITNESS TWITTER || FIND US ON FACEBOOK