Nashville’s alternative side dominated the Gentilly Stage on Thursday, opening the second weekend of the New Orleans Jazz and Heritage Festival presented by Shell.

First up was Sturgill Simpson, an independent artist who last year won over tastemakers with a sophomore album that adhered to the traditional side of country music not often found on commercial radio. At Jazz Fest, Simpson didn’t wear a Stetson or flex a ripped set of muscles, nor did he sing a single song about his truck. Instead, his 90-minute set was streamlined with poker-faced country ballads and honky-tonk rockers that, near the very end, included some psychedelic jamming.

Simpson played acoustic guitar, leaving the tasty licks to guitarist Laur Joamets, who used his Telecaster for fluent slide work and, on songs like “You Can Have the Crown,” some Sun Records-era riffing. Joamets was the secret hero of the set, adding speed and urgency to Simpson’s steady baritone vocals.

Together, they presented a heavier side of country music as originated by Merle Haggard and Lefty Frizzell, among others.

On “Life of Sin,” Simpson sang with a growl in his voice, offering lyrics as despondent as a Hank Williams tale of woe (“Every morning when I rise, I look in the mirror and despise/the sight of everything and all that I’ve become”), but the music never felt frail. Instead, like a bullet train, the band shot through its set, culminating in T Rex’s “Bang a Gong,” an unrecognizable cover version in double time.

Next onstage were Alison Krauss and her long-standing band, Union Station. It was the band’s Jazz Fest debut, and the band’s subtle playing style and precious three-part bluegrass harmonies disappeared into the open air of a festival stage. The acoustic perfection of concert halls and theaters is this group’s strong suit, but outdoors the music didn’t project and got lost.

Dobro player Jerry Douglass was a highlight, adding color to songs like “Let Me Touch You for a While,” a gentle ballad that was lifted by the harmonizing of Krauss, guitarist Dan Tyminski and guitar-banjoist Ron Block. The group played without a drummer, likely a good reason why the music didn’t get far past the stage. But if you were up close, you were rewarded by the rarefied musical interplay of acoustic instruments and vocals that illuminated each song.

The blues — minimalist and sanctified — arrived earlier in the day in the guise of Robert “Bilbo” Walker and The Word, a supergroup featuring steel guitarist Robert Randolph, keyboardist John Medeski and guitarist Luther Dickinson, drummer Cody Dickinson and bassist Chris Chew, of the North Mississippi Allstars.

Walker performed in the Blues Tent early in the day. The 78-year-old guitarist-singer lives in California, but his playing showed his Mississippi roots. Wearing a burgundy suit and with his wife, Estelle Walker, seated playing bass at his side, Walker chugged through 12-bar blues while wiggling his hips and duck-walking from one microphone to the next.

It was questionable why the trumpet player in his band needed to blow through two horns at once, but it sounded perfectly natural when the band launched into Chuck Berry’s “Johnny B. Goode,” giving the set a solid reference.

Soon afterward, The Word headlined the Acura Stage, playing a set composed largely of instrumentals set around Randolph’s steel guitar positioned in the center of the stage. The band drew from, and played off, the sounds he drew from the instrument. Despite a right wrist bandaged after an injury, Randolph summoned piercing notes from the guitar that launched into speedy boogies, moody soundscapes and gospel.

The surprise set of the afternoon was by New Orleans trumpeter-singer Shamarr Allen and his Underdawgs. At the Congo Square Stage, Allen spotlighted five young horn players he teaches in a community music clinic he conducts on the second floor of his parents’ home in the Lower 9th Ward.

One by one, the five took solos, as well as handling vocal duties on a cover of the Mark Ronson-Bruno Mars hit “Uptown Funk.” Their hands were tiny, but their spirits were mighty, as they won over the crowd with each verse.

Allen’s teenage son, Jarrell Allen, handled the drum kit for what became an uplifting segment of his father’s hourlong set.

“I feel like I’m part of something real, y’all,” the elder Allen told the crowd. “The future is right here.”