Lebo (ALO) and Jack Johnson- photo by Dean Budnick

A few minutes before 2:30am, Jack Johnson stepped onstage in That Tent to play a few songs with the evening’s final act, ALO. Though Johnson’s carefully disguised mini-set was planned as a casual way for Hawaii’s mellowest megastar to hang with his old pals before the release of his new studio album From Here to Now to You, his surprise appearance felt like a colorful nod to the festival’s beginnings.

Johnson was actually one of the breakout stars at the inaugural Bonnaroo way back in 2002, and he continued to grow with the festival right through a marquee headlining spot in 2008. His breezy, rainy afternoon Which Stage spot in 2005 and his acoustic What Stage jam with Eddie Vedder in 2008 remain some of Bonnaroo’s defining moments. So a post-midnight jam session in That Tent seemed like the perfect place to open the next chapter of his career.

Santa Barbara, CA’s ALO were also the ideal group to host his first Bonnaroo performance in five years. Not only does ALO singer/keyboardist Zach Gill play in Johnson’s band, but the members of ALO have known Johnson since college and are currently signed to his Brushfire records. Like their big name special guest, ALO have grown with Bonnaroo over the years and continue to embrace the Mardi Gras energy and collaborative spirit so essential to the festival’s core. Johnson casually waltzed onto the stage halfway through ALO’s set and joined the quartet for take on “Man of the World” and their best-known collaboration, “Girl, I Wanna Lay You Down.” Then, renowned photographer Danny Clinch appeared on harmonica with Johnson and ALO for “Falling Dominoes” and remained onstage as the song gently segued into Johnson’s “Better Together.” The early Johnson hit “Mud Football,” a throwback to his first Bonnaroo performance, capped off the late night appearance.

In addition to Johnson, husband-and-wife duo Nicki and Tim Bluhm, who share ALO bassist Steve Adams with their band The Gramblers, joined in on covers of The Rolling Stones’ “Tumbling Dice” and “Workingman’s Blues,” while ALO borrowed Ryan Montbleau Band percussionist Yahuba Garcia for the entire set. The rest of the Ryan Montbleau Band also sat in on a spirited version of Paul Simon’s “Graceland” during the show’s encore.

ALO’s guest-heavy performance capped off a day of surprise announcements. In some unfortunate news, Mumford & Sons have cancelled their Saturday headlining after bassist Ted Dwayne underwent emergency surgery earlier this week to deal with a blood clot in his brain. Though Dwayne is said to be recovering and had hoped to perform on Saturday, the group made the difficult decision to cancel the rest of their Summer Stampede Tour. Indie rock group DIIV were also forced to postpone their This Tent set after weather-related issues delayed their flight to Tennessee. DIIV will now perform in The Other Tent at 4pm today, replacing Earl Sweatshirt. The Odd Future member alerted his fans in an all lowercase tweet that read, “To everyone at bonnaroo: im sorry i cant make it im really really fucking sick but i will make it up to tennessee as soon as i possibly can.”

In a bit of more uplifting news, some lucky fans caught a bonus Paul McCartney performance. The Beatle arrived onsite with the help of a police motorcade around dusk and sound checked a few songs on the massive What Stage. While the concert field was closed off, a few lucky onlookers could hear Sir. Paul test out classics like “Magical Mystery Tour,” “Penny Lane,” “Being for the Benefit of Mr. Kite!” and “Eight Days a Week” as well as a jam where McCartney repeatedly sang “Bonnaroo.” “Eight Days a Week” is a particularly rare surprise: With the exception of one televised performance with The Beatles in the mid-‘60s, McCartney had never performed the song live before this spring. Later in the night, The Polyphonic Spree played a 2am pop-up show on Bonnaroo’s Fountain Stage after playing a live score for The Rocky Horror Picture Show in the Cinema Tent.

Veteran Bonnaroovians are accustomed to a Thursday night surprise or two. With a carefully curated blend of hard-touring young live acts and current blogger buzz bands, Bonnaroo’s Thursday lineup has long served as a showcase for tomorrow’s future headliners. The main What and Which Stages remain dark and campers are able to shuffle between stages like tracks on a iPod.

Bay Area roots group Nicki Bluhm & The Gramblers officially opened That Tent with a 60-minute medley of styles deeply engrained in Bonnaroo’s DNA: roots rock, folk, jam, indie, soul and country. They settled into a steady groove on “I’m Your Woman,” showed off their close harmonies on the delicate “In the Mountains” and proved their radio potential with “Jetplane.” A bit later, JC McPherson offered his update of ‘50s-style rock and roll. Meanwhile, Bridgeport, CT pop-polished funk-fusion trio The Stepkids tested their new single “The Lottery,” which was released just a few days ago, and offered as series of Steely Dan-inspired deep grooves that felt tied to Bonnaroo’s deep improvisational roots.

Others bands hooked new fans with creative covers. New Orleans singer Andrew Duhon nodded to his hometown with the Big Easy classic “St. James Infirmary Blues,” Indiana roots rockers Houndmouth offered a faithful John Prine tribute, returning Bonnaroo heroes Futurebirds found the southern soul in Stevie Nicks’ “Wild Heart” and anthemic indie rockers Milo Greene weaved both Sufjan Stevens’ “Chicago” and Wilco’s “Shot in the Arm” into their energetic set in That Tent.

For much of the day hip-hop and electronic music echoed throughout Centeroo. In The Other Tent alone, Ohio duo Twenty One Pilots filled in the spaces between rap rock and sythpop, AraabMuzik hyped the crowd with a series of infectious homemade beats, Purity Ring explored the more delicate, dream-pop side of electro-pop and rising Colorado EDM producer and performer Paper Diamond represented a generation of onetime Bonnaroo campers returning years later as performers. The smooth, electro-charged Capital Cities also played their anthem-in-the-waiting single “Safe and Sound” in the Club Stage.

Different strains of psychedelic music could also be heard throughout the day, too. In addition to Futurebirds’ psychedelic twist on county rock, Ariel Pink pushed the darker, post-punk-influenced edges of the new psychedelic frontier in This Tent. Former Fleet Foxes drummer Josh Tillman returned to Bonnaroo under his manic, crooner-gone-rogue Father John Misty alias. Swinging his mic. stand like an instrument, he serenaded the crowd with tracks like “Hollywood Forever Cemetery Sings” between a few choice one-liners. (Fellow sweet-voiced bear rocker Jim James watched from the stage’s wings.) Rhythmic English exports Django Django—who proved to be the missing link between the fest’s ravers and psych-rockers—reminded the crowd that art rock can still make great dance music .

The evening’s kaleidoscope of sounds also included Canadian rockers Japandroids, California sisters Haim, blue-eyed soul singer Allen Stone, experimental folk troupe Maps & Atlases and self-described “dad country” rocker Jonny Fritz, who performed in a neck brace following a recent skate park accident. The last member of the Middle Brother neo-folk supergroup to play Bonnaroo, Fritz completed a conceptual puzzle by playing Middle Brother’s eponymous song (the other members of Middle Brother are in Bonnaroo veteran acts Dear Tick, Dawes and Delta Spirit.)

In many ways, Alt-J served as the evening’s unofficial headliner. The melodic, Radiohead-schooled English indie rock quartet drew thousands of fans to This Tent, extending the sea of fans into Bonnaroo’s trademark multi-colored mushroom fountain. They offered singles like “Breezeblocks,” “Tessellate” and “Something Good” which elicited more than a few “best show of my life” tweets. Off the stage, Bonnaroo was also in all swing. Like the first day of camp, fans took in their new surroundings, greeted old friends and slowly detaching from the outside world as they moved further down the rabbit hole. As Bonnaroovians moved from stage to stage and style to style, the Magical Mystery Tour had begun.