The performance finale at the Nokia Theatre featured major contrasts – the old-school rocker with mega pipes against the teen powerhouse and first female wild-card pick to make it this far – as well as more drama than usual, as Johnson battled not only Irene but also an injured vocal cord.
Each sang three songs: a pick from Idol creator Simon Fuller, a contestant's choice and the original song that would be the crowned champ's debut single.
Round 1 saw Irene take on "Dog Days Are Over," and Keith Urban said she "[owned] that stage," but Johnson had Urban and Jennifer Lopez out of their seats performing Fuller's pick of "Dream On."
"That's what you gotta do! You gotta Carpe Diem, and you just did it!" said Lopez, although Harry Connick Jr. said he wanted to "see that crazy power" in the rocker's lower register.
In Round 2, Irene selected "Can't Help Falling in Love," the Elvis Presley tune that had Lopez near tears and rushing the stage a few weeks back, and the song again gave her goosies.
"Your soul comes through when you sing at the piano," said Lopez. "It makes me feel things I've never felt," while Urban called her a "trailblazer" and "true artist."
Johnson chose to re-sing "Maybe I'm Amazed," which Connick originally called "phenomenal," but the judges felt was a bit less than this time around, saying it lacked heart and emotion.
"It's a tie after two rounds!" Lopez said, after Connick prompted an impromptu vote.
And so it all came down to a single song, which was as different as each performer.
Irene's original "We Are One" was an up-tempo pop-dance tune that Urban "loved" and said was "perfect" for her, while Connick stated it was "just as strong as when you did it in the studio."
Johnson's winner's single, "As Long as You Love Me," was, of course, a rock song that had Connick comparing the two singers to Joe Frazier and Muhammad Ali, saying it was "a puncher vs. a boxer."
"I'm dying to see what happens tomorrow night," said Urban, while Lopez concluded, "Good luck, America!"
Who will take the title? Tell us who you think will be the next American Idol in the comments below.
The celebrity-studded finale airs Wednesday (8 p.m. ET) on Fox.