Same goes for Affleck's portrait of Robert Ford, a boyish, stammering sidewinder who joins up with the outlaw hero Jesse James in the title-says-it-all ''The Assassination of Jesse James by the Coward Robert Ford.'' Affleck, with an apologetic, snaggletoothed smile, almost steals the loping, picturesque Western out from under Brad Pitt.
''Casey's good, real good,'' says Pitt, who took the job as Jesse James. ''It's an amazing performance.''
In a hotel room on the eve of ''The Assassination of Jesse James'' premiere at the Toronto International Film Festival, Affleck, 32, riffled through a festival program guide ("Heard anything about this new Peter Greenaway?'') and fielded questions about his twin pics - pics that already have Variety enthusing that Affleck ''shows low-key but potent acting chops to be reckoned with.''
''I'm just so happy to be in something I really like,'' he says quietly, matter-of-factly. ''It's not often that you even get to read a script that you really like, let alone actually be in the movie. And for me to be able to say that now about two movies at the same time - well, it's been something special for me.''
In ''Gone Baby Gone,'' which was adapted from the Dennis Lehane mystery by Ben Affleck and Aaron Stockard - and then directed by Ben Affleck, making a confident behind-the-camera bow - Casey is kind of a working-class Beantown Nick Charles to Michelle Monaghan's Nora. The private-eye duo, who work together, live together and sleep together, get hired on an ugly case about a missing 4-year-old girl. Morgan Freeman and Ed Harris are two of the Boston cops pursuing their own investigation. The film, shot in some hardscrabble Boston neighborhoods, gets fiercely violent, and so, too, does its star.
''We shot 'Gone Baby Gone' about six months after Jesse James,'' says the actor, who lives in Los Angeles now, but grew up with the Affleck clan in and around Boston. His mother, who still lives there, was a teacher. His dad was a drug counselor, a mechanic, a bartender, an actor.
''It's a big advantage, playing a role in the place where you grew up, surrounded by the kind of people you grew up with,'' Affleck says. ''The accent, the attitudes, all of that was just totally familiar.''
About his brother, Casey says, ''I'm really proud of what Ben did, I think he did a great job directing. He's a natural leader, and people really want to follow him, but he also, like any good leader, knows when to follow himself. He's very collaborative.''
And Affleck is proud that his brother's directing debut is also a celebration of their hometown.
''Having grown up there, Ben had a firm grasp on the atmosphere, the environment there. And I think that that comes across. . . . We both love Boston, all parts of it, and I think that's evident in the movie.''