"It sounds like the whole world's singing," Paul McCartney beamed as tens of thousands of Beatles fans sang along to "Hey Jude" near the end of a long and winding road at the Austin City Limits Music Festival on Friday night in Zilker Park.

For a couple of hours, Sir Paul made it feel like everyone was together. A massive crowd started gathering at the American Express stage on the east side of the park about an hour before McCartney and his band went on at 7:45 p.m., and very few people left until the final note of the "Abbey Road" side two suite rang out just past 10 p.m.

A McCartney show is a marathon and not a sprint, especially as part of ACL Fest. Those who caught his two shows at the Erwin Center in 2013 had it easy compared to this, with cushy reserved seats and no need to jockey for position way ahead of time.

Many in the crowd — yours truly, for one — may have been fairly exhausted by the time the show began. And after an opening salvo that included the Beatles' "A Hard Day's Night" and "Can't Buy Me Love" plus Wings' "Hi Hi Hi," it took awhile before the set started to build again. There was the obligatory new single to play (the tepid "Come On to Me") and a lesser Wings number ("Let Me Roll It"), with Paul switching from his trademark "Beatle bass" to electric guitar.

You had to just remember: It's a marathon, not a sprint. When McCartney moved to piano for the lovely "My Valentine" from 2012's "Kisses on the Bottom" album, the volume may have gone down, but the quality was about to go way up.

The 1970s hits "1985" and "Maybe I'm Amazed" followed before a switch to acoustic guitar for a delightful skiffle-simple passage that began with the Beatles' "I've Just Seen a Face" and "From Me to You" as well as the fascinating R&B tune "In Spite of All the Danger" (recorded by proto-Beatles band the Quarrymen in the late 1950s). By the time they hit the first Beatles single, 1962's "Love Me Do," you could feel that second wind blowing through the crowd.

Emotions eventually got the better of just about everyone. For someone to my left, tears came on "Blackbird," which McCartney eloquently explained was written for Americans who fought for civil rights in the 1960s: "You were only waiting for this moment to be free." McCartney himself got choked up on "Here Today," written after the 1980 murder of his Beatles mate John Lennon.

For me, it was the photos of fellow departed Beatle George Harrison as McCartney segued Harrison's "Something" from ukulele to full-band glory that brought it all to bear. And later, in the "Abbey Road" suite encore, I looked to my right to see a young woman sigh sweetly to her boyfriend: "And I would sing a lullaby."

Oh, but I've skipped over that part where he played "Band on the Run" and "Back in the U.S.S.R." and "Let It Be," and then all the pyrotechnics and fireworks that accompanied "Live and Let Die." And that "Ob-La-Di Ob-La-Da" sing-along. And the encore-launching segue of "Sgt. Pepper" into "Helter Skelter." It was a marathon, indeed, and an unforgettable one.

At 76, Sir Paul sometimes strains to hit the high notes, and he punctuates each song with a ginger little jig befitting someone his age. McCartney has loved music the way the 18th-century classical masters did, and he's left us with that level of legacy. If he's a little tired, he has a right to be.

He has nothing left to prove. He's doing this for us now. Friday night, a park full of ACL Fest faithful accepted that gift, smiling and singing along. It's a moment we'll not forget.

And it all goes down again next Friday.