Readers’ Poll: The 10 Best ‘American Idol’ Performances

For disco week, Lambert turned a dance classic into a power ballad, belting out and slowing down Yvonne Elliman's song. As was Lambert's strength during his run on the show, his originality shined once more with help from his "immaculate vocals," as Simon Cowell described them.

Durbin made it to the Top Four on Season 10 but had already established himself as the resident metalhead. Over the course of the show, Durbin covered hard rock classics but none as soaringly as his take on Judas Priest's "You Got Another Thing Comin.'" Steven Tyler admired how over-the-top he was, and he called the performance "fucking crazy good."

During Motown week, Lambert was intimidated by mentor Smokey Robinson mostly because he was preparing to cover Robinson's "The Tracks of My Tears." At the show, the contestant gave one of his most tender performances, allowing his falsetto to shine while being accompanied by just an acoustic guitar. 

The show's Season Four winner wowed the judges and audience early by shifting from her country roots into a hard rock heroine for her delivery of Heart's "Alone." Right after her performance, Simon Cowell predicted that not only would she win her season but she would also outsell all previous winners.

Cook turned Mariah Carey's "Always Be My Baby" into a soft-rock slow jam. By the end, he had built it up into an anthemic and heavy version of the pop tune. Simon Cowell described it as "coming out of karaoke hell into a breath of fresh air."

The show's creator Simon Fuller chose the Sam Cooke classic for Lambert, and the singer who admired glam rock ended up being a surprisingly perfect fit for the passionate, bluesy, soulful song. While on her feet, Paula Abdul admired it as one of Lambert's best vocal performances and called his future career "iconic."

Lambert perfectly matched Robert Plant's vocal talent with his take on Led Zeppelin's "Whole Lotta Love," hitting every note and sexual innuendo with ferocious power. Afterward, Randy Jackson wanted a collaboration from the singer and guest Slash, while Kara DioGuardi hoped for a future Seventies classic rock and Eighties glam album from him. Simon Cowell's big concern was that "nobody can top that now."

Lambert felt that country wasn't exactly the right fit for him, so he made the genre fit him. The Grand Ole Opry week's guest coach, Randy Travis, was in shock at the Middle Eastern-infused take the contestant had on Johnny Cash's classic. Most of the judges admired his unique take, and Randy Jackson even described it as "Nine Inch Nails doing a country song."

Lambert's moody take on Tears for Fears' "Mad World" — done in the style of Gary Jules' piano cover for Donnie Darko — was a star-making one. He brought the theatrics that set him apart as a contestant but in a subtle way to match with the somber tone of the song, all while belting out the song for one of his strongest vocal performances on the show. Even Simon Cowell was on his feet at the end of it.

David Cook's take on Michael Jackson's "Billie Jean" was ideal: He took a pop classic and completely transformed it to match his own style. The rock winner of Idol's seventh season stripped down the tune until it was dark and brooding, similar to Chris Cornell's arrangement of the track, which served as the contestant's inspiration.