When the Beatles came to America in 1964, the Fab Four met a pretty fabulous two - Albert and David Maysles, still early in what would become one of cinema's most distinguished documentary careers.

The result was "What's Happening! The Beatles in the U.S.A.," which caught the Liverpool lads in an unscripted, humanistic portrait in a way Richard Lester's staged documentary-musical "A Hard Day's Night" could not.

Thirty-seven years later, Paul McCartney was stranded on a New York airport runway on 9/11. He spearheaded the Concert for New York City, an all-star benefit that would go off less than two months later. When the former Beatle decided to record the behind-the-scenes lead-up to the event, he picked up the phone and called Albert Maysles. (David died in 1987.)

The result is "Paul McCartney: The Love We Make," released in New York on the 10th anniversary of 9/11 and opening at the Roxie on Friday. (It was released on DVD and Blu-ray last week.)

"I saw John Lennon many times, and George Harrison a few times" since '64, Maysles, now 85, said by phone from his New York office. "But not Paul so much. ... Paul called and said, 'Look, in two weeks I'm putting together this concert to help overcome the stress of 9/11. Let's make a film and shoot it in black and white, just the way we had in '64, when the Beatles first came to America.' It was a sentimental touch."

Indeed, the black-and-white, 16mm film stock gives a timeless feel to "The Love We Make" (scenes from the actual concert are in color) and McCartney, then 59, exudes a boyish, Beatle-like enthusiasm for the event, which leads him on the interview circuit (Maysles captures behind-the-scenes time with Howard Stern, Dan Rather and others), walking the streets as surprised New Yorkers thrill at seeing a Beatle pounding the pavement, and working with his band in rehearsals.

Yet the footage Maysles shot was set aside, for various reasons. In 2009, Maysles received a handwritten note from McCartney asking if he thought there was a still a film that could be made. Maysles and his current filmmaking partner, Bradley Kaplan (who is credited as co-director), set to work.

Maysles, whose classic credits include "Gimme Shelter," "Grey Gardens" and "Salesman," and Kaplan spent two years preparing it for the 10th anniversary of 9/11.

"When I first looked at the footage, I said, 'This is the great unseen Maysles film,' " said Kaplan, an accomplished documentarian in his own right. "In the concert itself, when Paul is singing 'Yesterday' and Albert's camera goes from stage up to the spotlight, back to the audience, of people singing along to 'Yesterday,' and back to Paul onstage - it's just one of these long, beautiful Maysles shots that I don't think that any other cameraman has done with as much regularity. It's spine-tingling for me."

Chronicle contributor Ben Fong-Torres will introduce Friday's 7 p.m. show. The screening is co-sponsored by the Roxie and the Recording Academy San Francisco Chapter, and a portion of the ticket sales will go to MusiCares, a charitable foundation.

Starts Fri. Roxie Theater, 3117 16th St., S.F. (415) 863-1087. www.roxie.com.