Jack Johnson Honors Mumford & Sons at Last-Minute Bonnaroo Headlining Set
Jason Merritt, Getty Images Entertainment

"I wrote this song this morning," Jack Johnson, acoustic guitar strapped in his hands, told his thousands of onlookers at the 2013 Bonnaroo festival on Saturday night (June 15), "and I just wanted to share it with you guys."

PAUL MCCARTNEYBONNAROO PHOTOS
Bonnaroo Webcast: Watch Live
Saturday: R. Kelly, Bjork, Weird Al
Paul McCartney, Passion Pit Rule Friday
Jack Johnson Talks Last-Minute Set
Thursday Recap: Haim, Killer Mike & more
Full Bonnaroo Coverage

When the 38-year-old folk singer-songwriter casually tossed out the statement during his headlining set, the nonchalance came off as completely natural; of course Johnson, who nodded at the opportunity to fill in for Mumford & Sons' recently scrapped headlining show at this year's Bonnaroo fest and pulled a cohesive set together in less than 48 hours, could summon the time and dedication to write a quick ditty on Saturday morning and hone it enough for Saturday night.

The song, titled "Bonnaroo," essentially served as a recap of the unfortunate festival situation involving Mumford & Sons bassist Ted Dwane undergoing surgery for a blood clot on the surface of his brain, forcing the folk-rock stars to cancel their Saurday night performance at Bonnaroo. Johnson's quickly organized replacement status was mentioned in his new song, simply titled "Bonnaroo": "I had a late night gig with ALO... but then the phone rang, and things got strange/My low pro[file] was about to change."

Johnson, who performed at the first-ever Bonnaroo 12 years ago and also headlined the festival in 2008, was able to write a song with a solid coda ("What the hell, it's Bonnaroo!") and full-fledged accordion solo in a matter of hours, but none of that was surprising. The mid-set treat was simply the  cherry on top of a delightful headlining performance that no one could have seen coming one week ago. Johnson, whose four-piece band hadn't played an expansive show in over a year, completely committed to the challenge of filling in for Mumford & Sons without complaint or error, and even maintained his surfer-dude halo by showing love to the U.K. quartet with a shout-out and cover song.

Bonnaroo 2013 Video

"We want to dedicate this whole set to Ted Dwane and all of Mumford & Sons," Johnson told the crowd, who roared their respect back in his face. Over an hour later, Johnson and his crew were jamming on "The Cave," Mumford & Sons' Song of the Year nominee from "Sigh No More."

In the two hours of the Manchester, Tenn. festival given solely to him, Johnson blew through all of his signature songs while rarely deserting his mid-stage mic, including "Bubble Toes," "Flake," "Fortunate Fool," "Tomorrow Morning," "Breakdown" and his "Curious George" cut "Upside Down." He also played "I Got You," the lead single from his forthcoming sixth album "From Here To Now To You," and the new tune received an encouraging response.

After Mumford & Sons officially canceled their performance on Thursday (June 13), Johnson, who was already on hand at Bonnaroo to join ALO as a special guest on Thursday night, was asked to fill in as Bonnaroo's first-ever replacement  headliner.  "As soon as I said yes, I said, 'Holy shit. I gotta learn a lot of chords and a lot of words really quickly," Johnson said during a special press conference on Friday morning.

Johnson's impromptu Bonnaroo performance was indeed impressively organized in a short time period, and helped set up "From Here To Now To You," due out Sept. 17. Bonnaroo 2013 ends with Tom Petty & The Heartbreakers taking the stage on Sunday evening.