MANCHESTER, Tenn. (AP) — Bonnaroo began in earnest Friday with the rarest of double bills: Chris Rock followed by Metallica.

Metallica's Lars Ulrich and Kirk Hammett introduced Rock, and the comedian in turn introduced who he called "the baddest ... band in the world." Both acts were unlikely fare for the Bonnaroo Music & Arts Festival, which began in 2002 as primarily a jam band event.

But in recent years, Bonnaroo has broadened itself and brought more diverse fans to its 700-acre countryside site south of Nashville. Among the tens of thousands of festival-goers, Rock, Metallica and many other performers were very conscious of their entry into a tie-dyed world they seldom traffic in.

In a bit in his set about Prozac and other medications, Rock chastised the crowd, who he said was likely on "performance-enhancing drugs."

"You all should be ashamed of yourselves for taking antidepressants to see a comedian," joked Rock. "I am an antidepressant!"

Metallica also touted its cheerfulness.

"Do you feel good?" lead singer James Hetfield asked the crowd. "Metallica is here to make you feel better."

Performing on the main stage Friday night, Rock jumped right into his material, much of which he's performed during recent touring. Looking on backstage were many of the other comedians performing at the festival, as well as Jack White, whose band the Raconteurs took the main stage earlier in the day.

Rock worked the giant crowd without missing a beat in his timing, hitting on the election, Anna Nicole Smith and high gas prices despite the war in Iraq, ("If I invade IHOP, pancakes are going to be cheaper in my house," he said).

Metallica had a more difficult time winning over the crowd, which was head-banging but apparently not moshing. Hetfield repeatedly urged the audience to sing along. He asked, "We do have a few Metallica friends here, yes?"

Hetfield occasionally informed the crowd the titles of the songs they were playing and which album they were from. "That was `No Remorse' from `Kill `Em All,'" he said, an annotation that would have normally been completely superfluous for the band.

But Metallica is an exceptionally hard working band — they could be heard practicing backstage in a trailer shortly before their set. Eventually, they won the crowd over with their tenacity, as well as classics like "Sad But True" and "Enter Sandman," the latter of which was accompanied by pyrotechnics.

Like a jam band, Metallica has a fiercely devoted following and Hetfield alluded to this Bonnaroo-ness of Metallica: "We support live music ... and that's why we're here."

The notorious Tennessee heat that has in the past made Bonnaroo a chore was thus far bearable (after midnight, My Morning Jacket pulled out a cover of Sly and the Family Stone's "Hot Fun in the Summertime"). But by then, the rain that had threatened through much of the day finally fell.

One of Friday's big questions was whether M.I.A., the British electronic dancehall rapper, would show. She recently canceled her upcoming European tour due to exhaustion from touring, but still performed an energetic set at Bonnaroo. She repeatedly called it her "last show."

"This is my last show, and I'm glad I'm spending it with all my hippies," she announced.

Usually sold-out with an attendance of 80,000, this year's Bonnaroo hadn't yet reached capacity, but was overrun with tens of thousands of fans who came from far and wide to camp through the weekend.

"So is everyone having a nice communal experience?" Vampire Weekend lead singer Ezra Koenig asked the crowd. He later added, with perhaps some sarcasm: "You guys, I'm sure, have a full weekend in store of discovering yourselves and others."

The New York-based indie band Vampire Weekend was part of the relatively thin Thursday night slate that also included several comedians, a tradition of Bonnaroo. Janeane Garofalo and Zach Galifianakis were among those performing in the circus-style comedy tent.

"They asked me if I wanted to perform at Bonnaroo and I said, `Will there be a circus tent?'" joked Galifianakis. His comedy often intersects with music; he plays piano during much of his act and he's starred in music videos for Fiona Apple and Kanye West, who's performing late Saturday night at Bonnaroo.

Garofalo said the challenges for a comedian in such an environment can be many.

"Nothing is better for comedy than doing it during the day, having this kind of noise behind you and doing it in a circus tent," she joked.

Also to play Friday were the Raconteurs, Willie Nelson, My Morning Jacket and the Swell Season and the duo of Irish singer-songwriter Glen Hansard and Czech pianist Marketa Irglova — the stars of the film "Once."

Hansard said he's still adjusting to being the co-winner — along with Irglova — of the Academy Award for best original song ("Falling Slowly" from "Once").

"It's a new personality to try on or a new set of clothes to try on," said Hansard, who was less famous as the lead singer of the Frames. "Everything you've been is basically over. ... Sometimes it feels more comfortable having potential rather than having accreditation."

Source: AP