Credit: Erika Goldring/WireImage

Two years ago, when Marcus Mumford and his band were first scheduled to headline at Bonnaroo, many would have told you they were the biggest group in the world. Their two albums—2009’s Sigh No More and the wildly successful Babel in 2012—established the quartet as the defining act of this century’s folk-rock revival. But that headlining set never took place. The group canceled day-of due to bassist Ted Dwane undergoing emergency surgery to remove a blood clot in his brain.

So when the group finally headlined this year’s festival Saturday night, guitarist Winston Marshall and Mumford both addressed the incident. Marshall thanked Jack Johnson for filling in at the last minute; Mumford shared how good Bonnaroo has always been to the group.

The wait was worth it. The boys delivered a two-hour set for around 80,000 fest-goers, featuring “Snake Eyes,” “Ditmas,” and “Believe,” from their plugged-in new album Wilder Mind. And while that album has received mixed reviews, Mumford, Marshall, Dwane and keyboardist Ben Lovett unleashed a set that was tenacious, electric and at times profound. At one point, Mumford threw his drum kit off the stage and stood front and center, his finger pointed to the sky, throat thick with emotion.

By the time the group brought Ed Helms out to play banjo on “Awake My Soul” halfway through, it was pretty obvious we were watching something incredible: each member of the band was straight up testifying on their instrument. And the crowd was peaking with them, jumping up and down and singing the group’s familiar, heart-swelling choruses with all their might.

Later on, the group dipped into old favorites like “Roll Away Your Stone,” “I Will Wait,” and “Lover Of The Light.” Mumford seemed thrilled with the group’s performance—and the connection they had with the audience. “F–k, you guys!” Mumford shouted. “You’re good people!”

But just when you thought things couldn’t get better than their main set, Mumford brought out members of Dawes, the War on Drugs, Hozier and My Morning Jacket, plus photographer-musician Danny Clinch and Helms for the encore: a rousing version of “With a Little Help From My Friends,” written by the Beatles and made famous by Joe Cocker.

Heading into Sunday night at Bonnaroo, headliner Billy Joel has a tough act to follow.