TORONTO - U2 lead singer Bono and guitarist the Edge greeted screaming fans on the red carpet Thursday night as a documentary about the Irish rockers kicked off the 36th Toronto International Film Festival.

Bono, sporting rose-tinted glasses and a black jacket, said Canada has always been kind to his band.

"For whatever reason, in this country music plays an almost sacramental role," he said. "People here care about music. People are very thoughtful about music and giving new bands a break."

Asked if he'd be partying after the premiere, Bono boldly proclaimed: "We're going to burn your town to the ground!"

"From the Sky Down," helmed by Oscar-winning director Davis Guggenheim is the first documentary to open the fest.

Guggenheim is somewhat of a veteran of the Toronto movie marathon, but was clearly tickled by Thursday's spectacle.

"It's nice to have a couple of rock stars on either side of you," he said.

Festival director Piers Handling also seemed elated by the opening night atmosphere.

"It's so great to feel the energy," he said as he surveyed the scene. "I think (the U2) film is going to launch the next 11 days of this festival in a magnificent way."

In an interview ahead of the premiere, Guggenheim said he discovered one major drawback to directing a documentary about the biggest band in the world.

When it comes to U2, everyone's an expert.

"The downside of a movie like this is the audience thinks they know the subject -- people feel like they have a relationship already with the band," he said in a telephone interview this week from his Los Angeles office.

"The only way to sort of puncture that is to have tremendous access.... I just kept pushing to go deeper and deeper and deeper, and they went with it, which is really wonderful."

"From the Sky Down" captures the Irish rockers during what should have been a period of triumph following the release of 1987's worldwide smash "The Joshua Tree."

But as the documentary casts its lens back to that era -- using a mix of fresh footage, new interviews and a wealth of archival clips -- we learn that the band struggled to adapt to its rapidly expanding profile. Bono couldn't adjust to performing in stadiums, the band felt creatively drained and the group's marquee success led to a powerful backlash, particularly after the release of the 1988 documentary and companion live disc, "Rattle and Hum."

As Bono himself puts it in the film, the band appeared on the verge of imploding. And over the course of his lengthy interview process, Guggenheim says it became clear that U2 really was on the brink of breaking up ahead of their seminal 1991 album "Achtung Baby."

"Yeah, absolutely," said the affable director of "An Inconvenient Truth" and "Waiting for Superman."

"(Talking to) each one of them, you could just feel it."

And, of course, Guggenheim did talk to each member -- again and again and again, with the intimate one-on-one conversations taking place in such far-flung locales as Buenos Aires, Dublin, Berlin, Santiago and Winnipeg, with the discussions often lasting hours.

He also persuaded the band -- which also includes bassist Adam Clayton and drummer Larry Mullen Jr. -- to open their Dublin vaults and let him sort through personal footage and photos from the "Achtung" era, as well as the unused dailies from "Rattle and Hum."

All told, how many hours of film did Guggenheim sift through?

"I would say it was exactly a gazillion amount," he laughs.

Such boundless fact-finding extended to Guggenheim's interviews, too, which yield some candid results.

"Nothing was off limits in this movie," says the director.

"From the Sky Down" features the sometimes impenetrable U2 personalities at their most pensive and even vulnerable.

Bono is especially open. Consistently self-deprecating and funny, the 51-year-old seems keen on puncturing the band's reputation -- among naysayers -- for political sloganeering and self-serious zealotry.

He speaks with a mocking tone of his '91 stylistic reinvention, which saw him don his now-ubiquitous shades, a chic Elvis coiffure and a pair of rock-star leather pants. More seriously, he takes himself to task for his increasingly controlling presence during the 1980s, marvelling that he's not sure how the band tolerated his sometimes-suffocating micromanagement.

In fact, that seems to be the focus of Guggenheim's film -- not the factors that once threatened to split U2 apart, but instead the forces that have somehow kept them together for 35 years and counting.

As "From the Sky Down" informs us via an entertaining animated montage, most bands that rocketed to fame in the '80s have since burned up in the atmosphere. But one of the prominent themes of the film is how seriously the quartet treats its bond as a band.

Collaborators explain on-camera that the members of the group are uniquely sensitive to one another's feelings. At one point, Bono dramatically refers to an incident of every-man-for-himself self-interest as a "betrayal" of the band concept. Likewise, in one of the film's most revealing moments, he discusses Edge's divorce as a grave event for the entire band and their families, and not just for his lead guitarist, proving the foursome's unique level of closeness.

"I think at its core, that's what the movie is about -- how do these four individuals defy what feels like a law of physics when it comes to a rock band, the law of physics being that every rock band has to implode or explode," said Guggenheim, who had a prior relationship with the Edge after directing the 2008 rock doc "It Might Get Loud."

"They have endured not just as a memory, (but) endured as a thriving, creative force."

"From the Sky Down" also takes pains to explore that ephemeral creative energy, doing so at a critical time in the band's history.

When it came time to craft "Achtung Baby," the band really had no idea how to find what they were looking for -- but they knew they wanted something new. With a half-dozen albums of sweeping post-punk behind them, Bono and the Edge began studying electronic pioneers Kraftwerk and even the chart-unfriendly industrial sounds of such groups as KMFDM and Einsturzende Neubauten before retreating to Berlin with producers Brian Eno and Canadian Daniel Lanois.

Eventually, "Achtung Baby" would provide something of a pop revolution, incorporating the thick dance beats that were sweeping the rave and club scenes of the early '90s, combining them with swirling guitars, ear-candy effects and sturdy pop songcraft for a reinvention that would usher in a new era for the group.

But upon arriving in the German capital -- itself still fractured and reeling from the fall of the Berlin Wall -- the band was rudderless and adrift.

That changed when they stumbled upon the eventual hit "One," a process of creative discovery that's thrillingly recreated in Guggenheim's film. An archival rehearsal recording reveals the band methodically fumbling toward the song's unforgettable tune, with Bono diligently searching for the melodic sweet spot like a surgeon scanning for the exact place to make an incision.

Guggenheim was a self-described big U2 fan like so many others (though he says this was something of a disadvantage, because "it's better when you make a movie not to be a fan -- it gives you more perspective on things"), so this sequence was a joy for him to watch as well.

"(That) was a massive breakthrough -- when everything was going terrible, they wrote that song in a matter of minutes, and it became sort of the thing that carried them out of this dark time," Guggenheim said.

"They each talked about how that magic moment happened so eloquently that it became the centrepiece of the movie."

While the opening slot of a major film festival can be a pressure-packed position for a new film, Guggenheim at least has one potentially stressful event behind him -- the band has already seen the film.

Guggenheim screened the movie for the group in July and, once again, they seemed united in their reaction.

"I think they were blown away," Guggenheim said.

"I think it does go very personal and very deep. But I think they saw that in it, there was truthfulness to it. And to me, they say it in the movie -- if they're truthful, as long as they're being truthful, that's so important to them."

The Toronto International Film Festival runs until Sept. 18.