New Orleans — The annual music marathon that occupies New Orleans every spring opened Friday for the first of two music-filled weekends at the Fair Grounds Race Course.

Day 1 of the New Orleans Jazz and Heritage Festival featured one performance delayed by a year, John Mayer’s headlining set at the Acura Stage. Booked for the 2012 festival, Mayer had to cancel because of a throat ailment that sidelined him into silence for months.

“Sorry I missed you last year,” the singer-guitarist acknowledged early in his set. “Thank you for coming back.”

Mayer and his band’s show included songs from his rootsy 2012 album, “Born and Raised,” songs they no doubt planned to play last year. Even though Mayer is a pop star, the album’s country-funky “Something Like Olivia,” for instance, suits a deep-rooted music festival such as Jazz Fest just fine.

Mayer made more roots connections with a lively update of Muddy Waters’ “Got My Mojo Working.” The song became the guitar-rich duet that Bo Diddley and Joe Walsh never quite got around to playing.

Of course, it was Mayer’s more pop-oriented songs, including the quietly intense “Slow Dancing in a Burning Room,” that sparked the bigger reactions from his fans. There was still plenty of guitar jamming to come, though, including the jumping Mayer’s extended ride through the Grateful Dead’s “Going Down the Road Feelin’ Bad.”

Mayer’s Stevie Ray Vaughan-influenced guitar chops and a schedule heavy with exceptional guitarists made Friday’s Jazz Fest a guitar festival within a festival.

Much of the six-string action happened at the Blues Tent, beginning with the son of the late New Orleans blues star Guitar Slim. Rodney Armstrong, aka Guitar Slim Jr.

Dressed in a gleaming white suit and pink vest and tie, Slim Jr.’s show must be among the best, most focused Jazz Fest sets he’s ever played. And his vocal performance for “Pride and Joy,” a song identified with Steve Ray Vaughan, sounded close enough to Vaughan to be the late Texas singer-guitarist.

Slim Jr.’s special guest Allen Toussaint, the brilliant New Orleans songwriter, pianist and producer, joined him at the piano for a performance of Guitar Slim Sr.’s greatest hit, “The Things That I Used to Do.” Toussaint smiled as he uncharacteristically pounded out primitive piano blues and then, once the song ended, kissed Slim Jr.’s hand before making his exit.

Slim Jr., accustomed to playing much smaller venues than the Blues Tent and not having New Orleans music royalty sit in, told the crowd, “I feel like B.B. King up here.”

Bryan Lee, wearing his trademark billy goat beard and shades, followed Slim Jr. in the Blues Tent for what, he told the crowd, was his 28th Jazz Fest appearance.

“My favorite time of the year, right here in New Orleans,” the blind singer-guitarist said.

A veteran of the Bourbon Street music scene, Lee entertained with scorching blues and second-nature between-song banter. Of his inability to do fancy dance steps a la James Brown, he explained, “I’m too old, I’m too fat, and that’s that.”

That said, Lee, who recently hit a milestone birthday, wasn’t ready for a rocking chair. “I just turned 70, but I don’t feel like 70,” he said before launching the bawdy “Brail Blues Daddy.”

More mighty guitar players, John Mooney and Lafayette slide guitar virtuoso Sonny Landreth, followed Lee in the Blues Tent.

Meanwhile, the guitars played on at the Gentilly Stage when Swedish-born, longtime New Orleans resident Anders Osborne channeled the Grateful Dead during his epic opening song and jam. Moving to Crosby, Stills, Nash & Young’s “Almost Cut My Hair,” Osborne demonstrated his playing’s warm tone and fluid lines of rubbery, connected notes.

Two 2013 Grammy Awards winner, Cajun musician Wayne Toups and New Orleans’ Dr. John, played back to back Friday at the Acura Stage. It was also the Jazz Fest debut of Dr. John’s new band, the Nite Trippers.

Even if the new band, led by trombone player Sarah Morrow, may still be a work in progress, old pro Dr. John delivered his unmistakable musical uniqueness.

Performing several songs from “Locked Down,” the 2012 album that won him his fifth Grammy Award this year, Dr. John, of course, played piano, as well as an electronic keyboard that replicated the sounds that fill “Locked Down.”

It was especially cool for fans, though, to see Dr. John, in tune with the day’s many other guitar performances, pick up a cherry red Fender Telecaster for a performance of Earl King’s pre-funk New Orleans classics “Come On.”

Guitar, as all New Orleans music aficionados know, is the instrument Dr. John played before the piano.