Willie Nelson’s beat-up blonde guitar, a Martin classical acoustic named Trigger, has been on tour with the country icon since 1969. It shows. The guitar is battered, lined with scratches and grooves, and has a hole above the bridge.

Nelson, like Trigger, is remarkable for his longevity and weather-worn character. Still touring at the age of 86, the indefatigable country musician brought his Outlaw Music Festival to SPAC on Saturday, with special guests Bonnie Raitt, Alison Krauss and Brothers Osborne.

Although he cancelled much of his tour over the summer due to medical problems, Nelson seemed in fine form at SPAC, where he opened, as always, with the signature tune, “Whiskey River.” From there, Nelson’s headlining set just flowed, like the river of brown liquor in the song.

A Lonestar flag hung on the backdrop as the Texan rolled through classics: “Still Is Still Moving to Me,” “Beer for My Horses,” “Mammas Don’t Let Your Babies Grow Up to Be Cowboys,” “Good Hearted Woman” and “If You’ve Got the Money I’ve Got the Time.”

“Give it up for Merle,” Nelson said before performing “It’s All Going to Pot,” a song he recorded with Merle Haggard before the country legend died in 2016. The toe-tapping tune has a cynical political message and is – as with all things Willie – unabashedly pro-marijuana.

Nelson’s catchy tune, “Roll Me Up and Smoke Me When I Die,” had the levity of a joke but seemed just as likely to represent a true wish on his part. He rounded out his set with Hank Williams’ “Jambalaya” and timeless songs like “On the Road Again,” “You Were Always on My Mind” and “Georgia on My Mind” before saying goodbye with the rousing spiritual “Will the Circle Be Unbroken.”

How lucky we were to see the 86-year-old Nelson – the poet laureate of American music in braids and a red headband – bring his charm and good-heartedness to Saratoga Springs on a beautiful early September night.

R&B legend Bonnie Raitt and bluegrass fiddler Alison Krauss – two consummate professionals, with unmatched talent and beautiful voices – opened with flawless performances.

Raitt’s set with her band revisited her nearly 50-year musical career and some of her biggest hits, including “Something to Talk About,” “Have a Heart,” “Love Letter,” “Nick of Time” and “I Can’t Make You Love Me.” There were also more recently recorded tunes, like sultry INXS cover “Need You Tonight” and “Unintended Consequence of Love” from her latest album.

Krauss joined Raitt onstage for a duet on John Prine’s “Angel from Montgomery” that was just stunning. “I got a little verklempt doing that,” Raitt said after the chill-inducing song ended. She held her hand to her heart, clearly moved, before giving Krauss a big hug.

Krauss’ stellar set with her band elicited hushed reverence from the crowd on Nelson tributes “I Never Cared for You” and “Angel Flying Too Close to the Ground” as well as fan-favorite “Stay,” her reinterpretation of 1960s song “Baby, Now That I’ve Found You,” and older tunes “The Lucky One” and “Ghost in This House.”

A walk around the festival’s Outlaw Village in between sets by performers offered everything from tie-dyes and top hats to t-shirts for Willie’s Reserve – Nelson’s brand of cannabis grown by independent farmers that was advertised prominently throughout the festival.

Fans could even pose with a life-size portrait of Willie while holding props, like a “Free Willie” sign or a wooden middle finger.

Brothers Osborne, a six-piece roots-rock band featuring brothers and Maryland natives T.J. Osborne and John Osborne, opened the festival at 4:15 p.m. with a well-received set of straight-ahead bar-room rock. They got the crowd clapping along to spirited tunes like “It Ain’t My Fault.”