It's Rock Week on 'X Factor,' and Josh Krajcik performed the most rock 'n' roll rock song and delivered the most unabashedly rock 'n' roll performance.

While several of the judges and contestants took liberties with the definition of "rock" and selected songs that could only marginally be described as rock -- no names here, since viewers already know who they are -- Krajcik and his mentor Nicole Scherizinger chose the ballsiest and gnarliest song for him to sing!

Krajcik soared through a loud and proud version of Foo Fighters' aggressive rock anthem 'The Pretender.' We were sort of surprised that Dave Grohl cleared the song for usage, since he was adamant about denying the Foos' music to be used on 'Glee.' That said, Grohl won't regret his decision to allow the song to be used, since Krajcik rocked it with a capital "R."

Krajcik has already shown us what he can do with his husky, soulful voice, but he demonstrated a versatility, thanks to his edge and the hardness of his delivery of the Foo Fighters track. From his stage presence, to the way he sang, to his mic stand constructed of a heavy duty chain, Krajcik brought the rawk!

L.A. Reid told him that he was the one who really brought the rock, while Paula Abdul dubbed it the best performance of the night so far. Simon Cowell recycled a line from his verbal bag of tricks, and once again said, "It was bloody fantastic."

Watch Josh Krajcik Perform Foo Fighters' 'The Pretender' on 'X Factor'