Joel and Ethan Coen had almost given up on casting the lead for their film "Inside Llewyn Davis." The part, a folk musician in early 1960s Greenwich Village, demanded the elusive combination of someone who could both carry a movie and perform the songs central to the film.

Then they met Oscar Isaac.

"It just didn't happen until he walked in the room," says Joel Coen. "There was a point at which we wondered if we'd written something that was essentially impossible to cast."

The Coens have long been known for their casting acumen, but they may have outdone even themselves with Isaac, a 33-year-old, Juilliard-trained actor with a few notable credits to his name but nothing on par with a major Coen brothers release. The film was greeted ecstatically at the Cannes Film Festival at its Sunday premiere, with Isaac hailed as the festival's breakout star and a possible Oscar nominee.

"I finally got the shot," Isaac said in an interview. "And I got it in this context, which is more than I honestly could have ever imagined for myself."

In the film, Isaac plays Llewyn Davis, a character very loosely modeled on folk musician Dave Van Ronk. Despite his evident talent for personal songs with traditional folk influences, he's an artist just barely out of step with history. Bitter and increasingly frustrated, he's a raging failure, missing his moment, one instead grabbed by Bob Dylan.

For many, Isaac's story is kind of an inverse of Llewyn. He is a young actor who gets his chance — "his minute," says music supervisor T Bone Burnett — and takes advantage of it.

"The whole story is about a guy who never gets there," says Burnett, the frequent Coen collaborator. "And yet the actual person who's playing that guy, does it. He seizes that minute like a motherf-----."

Isaac isn't as sarcastic or as antagonistic as Llewyn: "My energy toward people is very much like 'I mean you no harm,'" he says. And he's trying not to get too far ahead himself with his rousing success at Cannes. His instinct, he says, "is always to diminish any good thing, so as not to be devastated later."

While Isaac says that he identifies with the role fortune and opportunity plays in catching a break, he more associates with the workmanlike attitude of both Llewyn and the Coens. For him, it was as much about gradually working toward "Llewyn Davis" as it was landing a single break.

"I remember when I was getting out of school, I was like, 'If they just gave me one shot. If they gave me the one shot, oh man, I know I can do it,'" he says. "Then I got my first movie and it came and it went, and I was like, 'If they just gave me one more shot, just another shot.' Then I started getting work, and I realized it's not about that. It's not about the shot. It's about work."

Born in Guatemala and raised in Florida, Isaac grew up playing in a variety of bands as a guitarist and singer, everything from ska to a hardcore band in which he sported blue hair. But since coming out of Juilliard, the New York actor has found his musical talents valuable in Hollywood. He also played a musician in the direct-to-DVD high school reunion comedy "10 Years."

His most notable previous credits include Madonna's British period film "W.E." and Nicolas Winding Refn's neo-noir "Drive," in which he played the formerly incarcerated husband of Carey Mulligan's character. (Mulligan co-stars in "Inside Llewyn Davis," along with Justin Timberlake.)

But when he heard about the Coens' film, he knew that his combination of skills was perfectly suited to the part.

"I said: I have to get a shot at this movie because I feel like my 33 years of life have been preparing me to do something like this," says Isaac.

He first submitted a recording of himself performing the traditional blues ballad, "Hang Me, Oh Hang Me," which Llewyn plays in the film. He auditioned for a casting director and then later for the Coens. Usually, as a guard against later disappointment, Isaac immediately tosses a script after an audition. But he didn't this time, and kept working on the part for the next month before Joel Coen called to tell him he got the part.

His preparation included performing the film's songs, like Llewyn, in downtown New York clubs. Buster Keaton was an influence in forming a "mask of melancholy."

"I would go to parties with that and try to interact with people with that," says Isaac. "It's tough because it's not about being cool. In a way, it's just about being very open and very up front with who you are. That was a scary place to live in."

But the music was central to character, a kind of window into Llewyn's soul. A bit of advice from Burnett (who also did the music for the Coens' "O Brother, Where Art Thou?") was crucial: "Sing like you're singing to yourself."

Along with Burnett, Isaac collaborated with Timberlake and Marcus Mumford. Using the parlance of musicians, Timberlake said Isaac "threw it down" in his performance.

"It felt like a little bit of serendipity," Timberlake says of the Cannes reception to Isaac. "Just seeing the looks on people's faces looking at him like, 'Where did you come from?' It felt like: 'Llewyn finally made it.'"

Moviegoers will surely become more familiar with Isaac when CBS Films releases "Inside Llewyn Davis" this December in the heart of awards season. (He also co-stars alongside Kirsten Dunst and Viggo Mortensen in the upcoming thriller "Two Faces of January.")

"Why this movie is so personal — I think to all of us — is because of the recognition that it just as easily can go the other way," Isaac says.

"There's very few geniuses that are shooting across the sky like Shakespeare or Dylan. The rest of us, it's like you have to work and be talented, but you got to be lucky for a lot of this stuff to happen."

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Follow AP Entertainment Writer Jake Coyle on Twitter at: http://twitter.com/jake_coyle