Duluth bluegrass band Trampled by Turtles proved why they’re still going strong after two decades Thursday night at St. Paul’s Xcel Energy Center. For lack of a better word, these guys rock.

Led by guitarist/songwriter Dave Simonett, the six-piece play acoustic stringed instruments — bass, banjo, mandolin, fiddle and cello — without a drum kit in sight. And they aren’t afraid to introduce elements of rock music to the very traditional bluegrass genre.

They’ve also become a staple on the summer festival circuit and established themselves as a strong opening act for the likes of Wilco, the Avett Brothers — who topped Thursday’s bill at the X — and Zach Bryan. As was in evidence at the X, the guys offer an unfussy, straightforward performance with a massive sound and a complete lack of showboating.

Songs like “The Middle,” which is faintly reminiscent of ’70s California soft rock, and “Midnight on the Interstate” showed how the band can build a surprisingly robust sound that makes them the perfect soundtrack for an outdoor summer show, preferably near a body of water.

Perhaps that explains the somewhat meager attendance at the St. Paul hockey arena in late October. A better fit probably would have been the Armory, where TBT made their debut two years ago to promote their Jeff Tweedy-produced album “Alpenglow.” Whatever the case, those who did show up got a terrific 90 minutes from TBT and two hours from the Avett Brothers.

Trampled by Turtles aired a few “Alpenglow” tracks Thursday, including the affecting “Quitting Is Rough.” They also did some deep dives into their early days, including 2004’s “Whiskey” and 2008’s “Darkness and the Light.” The crowd seemed to adore it all, but really lit up for rave ups like “It’s a War” and the group’s fiery instrumentals that hit like a freight train.

The sextet wrapped with two big ones. “Alone” came across as a deceptively simple ballad that blossomed into something much more rich and emotional. And their speedy rocker “Wait So Long” had the audience buzzing and, I’m guessing, making plans to catch TBT outdoors at some point next summer.

As for the Avett Brothers, their entertaining, well-paced set held the crowd in a thrall. They also showed how far they’ve come in terms of songcraft and staging, bouncing between wall-of-sound bangers and stripped-down and tenderly delivered ballads. Midway through the show, the pair reminisced about playing the Minnesota Zoo in 2009 and a joint 2016 Target Center show with Brandi Carlile.

Whether it was classics like “Head Full of Doubt, Road Full of Promise” or tracks from their self-titled 11th album — which has been seen as a course correction after 2019’s misguided “Closer Than Together” — the brothers performed with style, grace and an approachability they shared with the band that preceded them.