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– The massive AFI Amphitheater was dark Sunday save for seven dimly lit movie-set spotlights onstage and the faint dark blue of the sky in the horizon as nightfall arrived. Amid the vague amber glow of those lights, Bob Dylan was crooning "Once Upon a Time" like time had forgotten who he was.

Before too long, he tore into "Ballad of a Thin Man," one of his scorchers from the 1960s. And then the 20,000-some concertgoers here appreciated the significance of Summerfest, on the final night of its 50th anniversary as America's biggest music festival, booking two American music institutions — Dylan and Willie Nelson.

Actually, the program was billed as the Outlaw Festival, organized by Nelson, with appearances by Jason Isbell, Sheryl Crow, Nathaniel Rateliff, Margo Price, Lukas Nelson and, of course, Dylan and Nelson. Not that any of them are truly outlaws. Iconoclasts, though, definitely.

Even though Dylan opened with his Oscar-winning "Things Have Changed," the more apt theme was the standard "Why Try to Change Me Now?" "Why can't I be more conventional?" Dylan, 76, asked with the Cy Coleman lyric.

Because you're Bob Dylan and you do things your way. The Nobel Prize for Literature hasn't changed him or the way he approaches concerts. Perhaps the flow from his own classics to standards seems more seamless — or maybe we're more accustomed to him doing standards after five albums' worth.

On Sunday, Dylan, who hasn't performed in the Twin Cities since 2014, transformed the guitar showcase "Highway 61 Revisited" into a piano boogie, heated up "Summer Days" into a rock 'n' roll romp and re-engineered "Duquesne Whistle" into a jump blues complete with swingin' guitar by Charlie Sexton.

However, "Stormy Weather" threatened to be forgettable, and "Desolation Row" lacked its usual potency. But then Dylan ended the 15-song, 75-minute set with the always powerful "Ballad of a Thin Man" and nary a word, just a bow, with his hand touching his heart.

If Dylan looked natty in his white sport coat, black shirt and bolo tie, two-tone cowboy boots and black pants with a white stripe, with curly, bedhead hair, then Nelson was Mr. Casual. He had his usual jeans, T-shirt, bandanna, braids and weathered acoustic guitar.

Unlike at his recent appearance at Treasure Island Casino in Red Wing, Nelson, 84, was in good spirits and voice; he was focused and personable. He also played lots of guitar, including the gorgeous Django Reinhardt instrumental "Nuages" and a splendid jazzy country passage during "Bloody Mary Morning." His band also included his son, guitarist Lukas Nelson, who did not appear at Red Wing.

Lukas Nelson added a bluesy bite, especially on a crowd-thrilling version of Stevie Ray Vaughan's "Texas Flood." Crow, Price and Amanda Shires from Isbell's band joined Willie Nelson on "Still Not Dead," "Roll Me Up and Smoke Me When I Die" and "I'll Fly Away," which made a festive finale for the nine-hour program.

Earlier in the evening, Isbell delivered a terrific, compact set of Americana. He brought urgency and musical variety in a quick hour, including a rip-roaring tribute to the late Gregg Allman, the Allman Brothers' classic "Whipping Post," ending with Isbell's trippy guitar work.

Crow also saluted Allman with "Midnight Rider," a duet with Lukas Nelson at the end of her set. Her performance reminded fest-goers what a deep skill set she has (singer, performer, bassist, guitarist, songwriter). However, her new song "Be Myself" is not strong enough to be a hit.

Rateliff, a hardworking, Van Morrison-inspired R&B shouter from Colorado, proved his bona fides with the tight, always entertaining Night Sweats, who weren't daunted by performing in broad daylight. They clearly have more experience than Lukas Nelson, whose songwriting didn't measure up to his considerable guitar skills.

As for Price, she may not be ready for big amphitheaters, but she has an affinity for wordplay and old-school country that will serve her well in honky-tonks.

This is the second year Nelson has taken the Outlaw Festival on tour. The artists vary from city to city. Among the others on tour this year are Van Morrison, Eric Church, My Morning Jacket, the Avett Brothers and Blackberry Smoke. But for its big Summerfest anniversary, Milwaukee landed a special lineup.

jon.bream@startribune.com 612-673-1719

Twitter: @jonbream