NEW YORK (Reuters) - Michael Keaton hung up his "Batman" cape more than two decades ago, but the versatile actor soared to new heights with a high-octane performance as a has-been trying to revive his career in comedy-drama and early Oscar favorite "Birdman."

In the film by Mexican director and Academy Award-nominee Alejandro Gonzalez Iñarritu ("21 Grams," "Babel"), which opens in U.S. theaters on Friday, Keaton plays actor Riggan Thomson, who like himself found fame playing the superhero in an action franchise he left years ago.

But Riggan is haunted by his Birdman super ego and a sense of failure and mediocrity, and makes a desperate attempt to regain his professional credibility and sense of self by mounting a play on Broadway based on the Raymond Carver short story, "What We Talk About When We Talk About Love."

"He's a really complicated character, which always makes the job harder, but more interesting, too," Keaton, 63, said in an interview.

"Birdman (or The Unexpected Virtue of Ignorance)," is a film about a play that Iñarritu ingeniously shot at Broadway's famed St. James Theater in what seems like one long, seamless, continuous take.

It was new territory for both the director and his cast. Each scene flows into the next as the camera follows Riggan down narrow theater hallways, into a dressing room, onto the stage and out of the theater into a bustling Times Square with drum rhythms setting a pounding pace.

Keaton said he had never seen a movie like it and admitted there were times when he wondered why they were doing it that way, which required plenty of rehearsals, no room for mistakes and total commitment from the actors.

"The truth is, it doesn't work if you don't make it like this because you don't go on the trip. You couldn't get as deep inside," Keaton explained.

"There is a point early on where you are watching this movie and quietly you hear the door close behind you, and you are not getting out now. You're in. Then you go into the guy's head."

Keaton delves deep into Riggan in a performance that has won stellar reviews, and which Variety called "the comeback of the century."

"Michael Keaton bursts into Oscar race with 'Birdman'," the Hollywood trade magazine proclaimed in a headline.

Keaton said one of the smartest things Iñarritu did was to present the cast with a photo of the French high-wire artist Philippe Petit, who famously walked between theWorld Trade Center's twin towers in 1974.

The meaning was not lost on Keaton and the cast, including Riggan's combative co-star Edward Norton, his leading lady Naomi Watts and Emma Stone, his daughter and assistant, recently released from rehab.

"You feel like you could fall," Keaton said, adding the film distributed by Fox Searchlight Pictures was choreographed down to the inch at times.

"But I like that. It keeps you on your toes. There is no time to get lazy."

Tags: Michael Keaton Emma Stone birdman movie