In its first major U.S. outdoor festival date in several years, Metallica ran through a blistering, two-hour set Friday (June 13) to headline the first official day of music at the seventh Bonnaroo mu

In its first major U.S. outdoor festival date in several years, Metallica ran through a blistering, two-hour set Friday (June 13) to headline the first official day of music at the seventh Bonnaroo music festival in Manchester, Tenn.

Augmenting its appearance with a slew of pyrotechnic explosions and even fireworks -- thus marking one of several Bonnaroo firsts during the festival experience Friday -- the world's biggest metal band mainly played its most popular and heaviest material (from "Master of Puppets" and "Creeping Death" to "Harvester of Sorrow" and "One"), plus the vintage covers that have become fan favorites (the Misfits' "Last Caress," Anti-Nowhere League's "So What").

Sweating through its clothes, as pretty much every artist did Friday in the 90-degree heat, Metallica repeatedly delved into 1991's massive "Black Album," and when it did, Bonnaroo experienced a collision of worlds, as young hippie girls and guys danced beside metalheads, singing every word to "Sad But True" and "Enter Sandman."

Routinely as much a part of Bonnaroo as the music, Mother Nature played just as big a role Friday, too. Rain drizzled during Metallica's set before pouring after midnight, soaking the thousands lined up in front of the festival's second biggest stage for an epic My Morning Jacket set.

During Tegan & Sara's early afternoon set, Tegan Quinn applauded the crowd for braving the oppressive heat: "I thought about coming earlier, but I would rather be in my hotel room in my underwear with the AC on 64," she said.

In one of the most anticipated performances of the weekend, Bonnaroo vets My Morning Jacket offered up a three-hour extravaganza featuring all but two songs from its brand new album, "Evil Urges." The first half of the show culminated with a rendition of "One Big Holiday" featuring Metallica guitarist Kirk Hammett.

With Les Claypool, members of Gogol Bordello and Hammett conjuring the festival's annual "Super Jam" in one tent, and DJ Tiesto enducing thousands of drenched fans to pogo to remixes in another, MMJ returned with a horn section and a trio of classic soul covers for another set.

It began with James Brown's "Cold Sweat," which found singer Jim James wearing a cape and sliding across the stage, and was quickly followed by Kool and the Gang's "Get Down on It," and Bobby Womack's "Across 110th Street." The epic performance closed with a cover of Motley Crue's "Home Sweet Home," with comedian Zack Galifianakis adding an additional festive touch by appearing on stage dressed as Little Orphan Annie.

While Bonnaroo has featured comedians for years, they've always performed in a dedicated comedy tent. But Friday marked the first time a comic has moved to the festival's biggest stage, as Chris Rock performed before Metallica, and later introduced the band, eliciting thunderous cheers from the assembled throng.

As much as Friday marked a series of firsts for the seven-year-old Bonnaroo, much remained the same, as some of the faces who have shown up repeatedly at the four-day fest popped up again. Indeed, Claypool quipped during his daytime set, "This is actually my 13th Bonnaroo."

Bonnaroo day one was another incredibly diverse display of music, featuring country's music biggest star, a member of reggae's first family, a bluegrass jam and everyone from The Raconteurs and Rilo Kiley to Chicago jam band faves Umphrey's McGee and Sri Lankan pop sensation M.I.A. (who claimed she was playing her "last show").

Willie Nelson's greatest hits set thrilled a crowd that spanned generations, one that hooted and hollered throughout. When he would slyly switch up a line or two, like flipping "Mama don't let your babies grow up to be cowboys" to "Mamas don't let your cowboys grow up to babies," the crowd roared, and the enduring icon blushed.

Earlier in the day, Stephen Marley opened the main stage, running through a mix of his father's most famous fare ("Buffalo Soldier," "Jammin'," "Get Up, Stand Up"), as well as such standouts from his recent solo debut, "Mind Control," such as "The Traffic Jam."

A mostly female audience swarmed the biggest tent and demanded encores during a performance from the Swell Season, featuring Glen Hassard of the Frames and Marketa Irglova, his co-star in the Oscar-winning film "Once.

Bonnaroo rolls on today with a headlining performance from Pearl Jam as well as sets from Jack Johnson, B.B. King, Mastodon, Cat Power, Levon Helm, Little Feat, Kanye West and Phil Lesh.

For additional Bonnaroo coverage, visit the Billboard blog at JadedInsider.com.