Long before Steve Carell was showered in acclaim for his startling transformation into John du Pont for the true-crime drama "Foxcatcher," he was walking home from set, commiserating with co-star Mark Ruffalo.

"We both looked at each other really in agreement that the whole thing was crazy and what we were doing was so far out there," Carell recalled in a recent interview. "We both felt we were taking huge swings."

You, too, might be a tad nervous about how you'd come off if you were — like Carell — fitted with a prosthetic nose, covered in three-hours of makeup, and asked to portray, with somber severity, an increasingly psychotic, chemical empire heir with both a raging mother complex and a proclivity for sweat pants.

Bennett Miller's "Foxcatcher," in which du Pont tragically befriends Olympic wrestler brothers Mark (Channing Tatum) and Dave (Ruffalo) Schultz, certainly had the potential of failing to pin down its stranger-than-fiction tale and leave Carell flopping on the mat.

"We weren't going to go halfway with it. That would have ended up being nothing," Carell says. "We both felt very vulnerable, that it could potentially be the worst thing we'd ever done or the best, but there was little in between."

More On This...

The needle has clearly swung to "best." Carell's performance has been hailed as one of the most extraordinary of the year, one immediately inducted into the rich history of comedic actors veering into dramatic territory. Carell, who was named the most outstanding performer of the year by the Santa Barbara International Film Festival, is considered a shoo-in for a best actor nomination.

"It's definitely darker than most anything I've ever done," Carell said. "The fact that Bennett had faith in me to do it, that was really a reward in itself, getting that kind of affirmation from someone like that."

Miller, the director of "Capote" and "Moneyball," was attracted to the idea of casting du Pont — who was convicted of murdering Dave Schultz on his family's 800-acre Foxcatcher estate in Pennsylvania in 1996 — with not an overtly villainous actor. Instead, he was drawn to Carell for his unthreatening demeanor and reputation.

"I did believe in my heart that if it could work with Steve, that that would be the best for the film," says Miller. "I couldn't imagine something working better than if that could work. I did have glimpses of it in just talking to Steve about the character and hearing his commitment to do it."

Since Carell's big-screen breakthrough in "The 40-Year-Old Virgin," the 52-year-old Second City alum has regularly mixed comedy and drama in films like "Little Miss Sunshine," ''Dan in Real Life" and "The Way, Way Back." But the considerable step Carell takes into darker terrain in "Foxcatcher" wasn't premeditated, the former "Office" star says.

"I didn't want to work at convincing people that I could do this," says Carell. "I just wanted to play the guy and try to do the best representation of this human being that I could. I didn't want that added sense, 'Oh, I hope people buy me in it' because people haven't necessarily seen me do this type of thing before. So I had to get past that and just do it."

Doughy, balding and speaking with a halting, presumptuous air, Carell is nearly unrecognizable as the removed-from-reality du Pont, who in the film is a symbol of the unchecked power of wealth and patriotism run amok.

Carell's old "Daily Show" boss, Jon Stewart (whose own drama, the film "Rosewater," reunited the two on the release calendar), says his former correspondent's gift for fleshing out a character was the same in a sketch: "He would find moments in it that you didn't know were there."

In shaping du Pont, Miller and Carell discussed Jerry Lewis' creepy stalker from "The King of Comedy," a renown dramatic pivot for the comedian. Carell cites Peter Sellers and his "Little Miss Sunshine" co-star Alan Arkin as actors he idolizes for their ability to range from broad comedy to serious drama.

Much of "Foxcatcher," for which Carell somewhat remained in character during shooting outside Pittsburgh, remains a kind of out-of-body experience for Carell.

"It's strange to talk about because it was one of those experiences that seems so isolated from the rest of my life. I feel like that was three or four months and then it was gone," he says.

But the film has clearly emboldened Carell.

"I don't want to play it safe going forward," he says. "I would rather do things that are interesting and are possibly a little bit dangerous and maybe unexpected and maybe things that are a little bit out of my comfort zone. That's an exciting thing to try. It's challenging. The experience definitely primed me for challenging myself."

WATCH: Four4Four: Is Bill Cosby's career J-E-L-L-Over?