The first night brought with it a Black Sabbath cover featuring Zac Brown. Night No. 2 had the Wilson sisters of Heart rocking ‘Kick It Out.’ And now, the third night (Oct. 15) of the Foo Fighters’ weeklong residency on the ‘Late Show With David Letterman’ produced the best performance yet: Tony Joe White joined Dave Grohl and company for a rendition of 1968's 'Polk Salad Annie.'

While Grohl took a step to the side for the first half of the song and let White handle the vocal duties, he stepped up for the second verse and laid down his own take on the classic swamp rock blues ballad. Paul Shaffer and the CBS Orchestra even lent their musical talents to the performance -- you can see it all in the video above.

At the end of the song, in true Letterman fashion, he walked onstage and emphatically said, "Unbelievable. That was fantastic. This is the guy here, oh my God, Tony Joe White. Holy cow." Making his enthusiasm for the song even clearer, he pointed to White and said, "I'll tell you something, and this is just between us: If I was this guy, you could all kiss my ass."

Before delivering the night’s Top 10, Letterman took a moment to share how much he appreciates the Foo Fighters. “Let me just say one thing about how great the Foo Fighters are,” he said. “It’s just great to have them. Each night they have a special guest performing with them as is represented from their new CD -- which is fantastic -- and the documentary of the making of this music on HBO.”

When it seemed like he was getting a little too mushy, Letterman introduced a new TV commercial that put it all into perspective: an ad for the offices of Grohl, Hawkins, Mendel, Shiflett, Smear and Associates. Their slogan? “We fight Foo for you.” Check it out:

On tonight's (Oct. 16) episode of 'Fooapalooza' -- as dubbed by Letterman -- the Foo Fighters will be joined by Rick Nielsen of Cheap Trick.

Michael Buckner, Getty Images

The Foo Fighters are gearing up for the debut of their eight-episode series on HBO, ‘Sonic Highways,’ this Friday, Oct. 17. A couple of weeks later, on Nov. 10, their latest full-length album of the same name will hit store shelves. Get details on the RCA Records album here.

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