"They're powerful, you know," McCartney tells Rolling Stone. "It's a great power to have them on stage with you. I mean, my band's great � but when you augment it with Nirvana, that's greater."

Nirvana's Grohl, Novoselic and Smear teamed up with McCartney at Safeco Field to perform an encore set of songs that included their original collaboration, "Cut Me Some Slack" (from the Sound City soundtrack), along with Beatles gems "Get Back", "Long Tall Sally", "Helter Skelter" and show closer, the "Golden Slumbers" medley.