Paul McCartney & Neil Young Jam on 2 Beatles Classics & a John Lennon Anthem at Desert Trip Day 2

Kevin Mazur/Getty Images for Desert Trip
Paul McCartney and Neil Young perform onstage during Desert Trip at The Empire Polo Club on Oct. 8, 2016 in Indio, Calif. 

Even though Desert Trip doesn't play by the rules of most music fests -- there are only two acts per day, the first one doesn't go on 'til sunset, and there are more people sitting than standing -- there's one rule for music fests in the 2010s that Oldchella does abide by: You gotta have a surprise collaboration.

So for Paul McCartney's Saturday (Oct. 8) night set in the Indio desert, the former Beatle brought out his opening act Neil Young for a three-song collab that had eyes wide and phones in the air.

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Describing him as "a really good friend," McCartney brought Young (fresh off a sick Trump burn) out to trade vocals on "A Day in the Life." Hearing Neil Young deliver "he blew his mind out in a car" in his unique timbre was treat enough, and the green fog swirling around the two as they sang the Sgt. Pepper's classic gave the existential rock song an additionally eerie layer. Instead of finishing the song with the usual orchestral climax, they transitioned directly into John Lennon's solo anthem "Give Peace a Chance," inviting the audience to chant along as peace signs flashed on the screen behind them.

After that mashup wrapped, Young stayed on stage, eliciting gleeful squeals from the crowd. As it turns out, the excitement was justified. While Paul and Neil have done the "A Day In the Life"/"Give Peace a Chance" mashup before, what came next was brand new.

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"Come on Neil, you gotta solo on this one for me," Macca said before launching into "Why Don't We Do It In the Road." Aside from the thrill of hearing McCartney do a song that's not part of his typical set list, Young's guitar solo was an unhinged scorcher. While McCartney's live shows never disappoint, his onstage consistency means that a sense of musical spontaneity gets sacrificed sometimes. So when Neil Young unleashed a wicked, razor-sharp guitar solo on The White Album track, the set felt -- for a moment -- dangerous.

Watch McCartney and Young trade guitar licks below. 

As for the rest of McCartney's set, Sir Paul was a consummate pro, delivering the many, many hits fans wanted to hear and jovially joking about the new stuff. "We know what songs you like hearing," McCartney told the crowd. "It lights up with your phones like a galaxy of stars during certain songs, like Beatles ones. When we play one you don't know, it's like a black hole. So here's another black hole," he quipped before launching into "Queenie Eye" from his latest album New.

Even so, the newest song in his set actually garnered quite an excited response. Macca delivered his Rihanna/Kanye West collab "FourFiveSeconds," causing the younger members of the crowd to get their phones ready in case Rih or 'Ye emerged. Neither did, but the real surprise was what happened next: Several Baby Boomers in the crowd begrudgingly murmured, "That actually is a pretty good song" to each other. Giving peace a chance is easy for the Woodstock set. But giving Yeezy a chance? That's a minor miracle.

Check out McCartney's full Desert Trip set list below.

A Hard Day's Night
Jet
Can't Buy Me Love
Letting Go
Day Tripper
Let Me Roll It w/ Foxy Lady (Hendrix cover) outro
I've Got a Feeling
My Valentine (dedicated to his wife: "We got our wedding anniversary tomorrow, so this one's for you Nance!")
Nineteen Hundred and Eighty Five
Maybe I'm Amazed
We Can Work It Out
In Spite of All the Danger (Beatles' first demo)
I've Just Seen a Face
Love Me Do (Dedicated to George Martin)
And I Love Her
Blackbird
Here Today (Dedicated to John Lennon)
​Queenie Eye
Lady Madonna
FourFiveSeconds
Eleanor Rigby
Being for the Benefit of Mr. Kite!
A Day In the Life/Give Peace a Chance (John Lennon cover) with Neil Young
Why Don't We Do It in the Road with Neil Young
Something (George Harrison cover)
​Ob-la-di, Ob-la-da
Back in the U.S.S.R.
Let It Be
Live and Let Die
Hey Jude

Encore

I Wanna Be Your Man
Helter Skelter
Golden Slumbers/Carry That Weight/The End