The annual, sun-drenched music-marathon that is the Bonnaroo Music and Arts Festival kicked off its fifth year yesterday (June 16) with more than 14 hours of music. First-day highlights included Stevi

The annual, sun-drenched music-marathon that is the Bonnaroo Music and Arts Festival kicked off its fifth year yesterday (June 16) with more than 14 hours of music that began with the resurrected folk-rock of World Party and finally lurched to a halt early this morning with the conclusion to a jam band face-off featuring Umphrey's McGee and the Disco Biscuits.

In between, the deeply and increasingly eclectic festival began to spread its creative wings with sets from bluegrass torchbearer Ricky Skaggs, alt-rock sensations Death Cab For Cutie, "it" troubadour Bright Eyes and a hip-hop triple bill featuring Common, Lyrics Born and Blackalicious.

Indeed, if in its first fours years, the festival (sold-out this year at 80,000 people) has been known primarily as a jam-band event, last night's bill should do well to help redefine the event, as Bonnaroo's behemoth main stage featured not only one, but two classic rock icons: Tom Petty and Stevie Nicks.

Last night's headliner, Petty welcomed Nicks onstage to reprieve their hit '80s duet "Stop Draggin' My Heart Around," and for several more songs, including the Petty staple "I Need to Know," sung by Nicks, who is performing this mini-set with Petty at each stop on his current U.S. tour. Ironically, during their two-hour-plus set, Petty and his Heartbreakers covered the pre-Nicks Fleetwood Mac rocker "Oh Well."

But of course there were jam bands, and with them plenty of the collaborations define Bonnaroo. The highly anticipated Umphrey's McGee and Disco Biscuits double-bill found the bands merging their sets, a transition where classic rock's appearance was felt once again. Opener Umphrey's played an hour-and-a-half before welcome the Disco Biscuits onstage for Pink Floyd and Beatles covers, which bled into the Biscuits' two-hour set. Joe Russo of emerging jam hot-shots the Benevento/Duo and Tom Hamilton of newcomers Brothers Past sat in for Floyd's "Eclipse."

Indie rock icon and jaded New Yorker Bright Eyes (Conor Oberst) adapted impressively to the surroundings, leaping into the spirit of Bonnaroo by bringing out lauded alt-country chanteuse Gillian Welch and her harmony partner/guitarist David Rawlings onstage for a few songs, one also featuring vocals from My Morning Jacket frontman Jim James. Gruff Rhys, leader of the Super Furry Animals, also guested, backing Oberst and even delivering a solo acoustic track midway through the Bright Eyes set.

Yet while much of the Bonnaroo collaboration magic happens on the fly, the highlight teaming of last night wasn't exactly spontaneous. It was announced: Oysterhead, the supergroup side project featuring former Police drummer Stewart Copeland, ex-Phish frontman Trey Anastasio and Primus bassist Les Claypool, reformed for the first time since 2001 and offered a mighty performance on the mainstage.

In the many tents, Devendra Banhart, Cat Power and ex-Phish bassist Mike Gordon drew big numbers. Dubbing his band the "Tennessee Cops," Banhart seemed less nuvo-folk and more nuvo-Jim Morrison, wowing festival-goers shirtless and with ample necklage. Banhart and company at one point welcomed a fan onstage, while also previewing the new tune "Right Reggae Troll."

One of the heroes of the day was Cat Power (aka Chan Marshall), who, flanked by the Memphis Rhythm Band, beautifully recreated her acclaimed new disc, "The Greatest." In top spirits, Marshall skipped and bounced onstage as her crack soul band rocked behind her. In true old-school rock fashion, Marshall had the band play a few numbers prior to her arrival onstage. She also gave the group (featuring horns and backing vocalists) a lengthy break during her many solo numbers, each met with roars of approval from exhausted, bikini-sporting revelers.

Bonnaroo favorites My Morning Jacket ushered in the midnight hour with squalls of Crazy Horse-worthy fury. The quintet delivered a more than three-hour set that sported a guest turn from friend and singer Andrew Bird for an epic take on another classic rock moment, "It Makes No Difference" by the Band. MMJ recently recorded the track for an upcoming Band tribute album at singer/drummer Levon Helm's barn studio in Woodstock, N.Y.

As the night neared a close, celebrated rapper Common could be heard paying tribute to the art of scratching and paying respect to the root of hip-hop -- the DJ -- as My Morning Jacket roared on the other side of the festival grounds.

For more Bonnaroo coverage, visit Billboard's Jaded Insider blog.