"But Jude Law's not in danger of me getting his parts, right?" drawls Giamatti. "Yeah, Jude doesn't need to watch his back right now." One senses Giamatti's humility is reinforced, after years of bit-parts, by an unburdening sense of relief. "Yeah, it's kind of nice to be in the leading man category," he concedes. "There's only a certain amount of time that you can put up with being the funny chubby guy."
Giamatti's performance as the cartoonist Harvey Pekar in American Splendor, the sleeper hit of last year, had critics and audiences salivating, but it was not until the release of Sideways, the offbeat story of a wine buff (Giamatti) on a road-trip into the wine regions of Santa Barbara with his college buddy (Thomas Haden Church), that the world sat up and paid attention.
British critics have called Giamatti's portrayal of Miles "glorious" and "the performance of his life". But for the man whom many in the film industry feel was criminally overlooked for an Oscar nomination last week, acting was not always a sure thing.
"I was in college, and a friend persuaded me to do a play. I wasn't a drama major or anything - it was all very extracurricular," he recalls. "Then I moved to Seattle intending to do something in the animation business, but I knew a guy who ran a theatre out there. I started making a living out of acting. I thought, `Well, I'm making money and I'm enjoying it, so I'd better keep doing it. Anyway, this isn't such a bad second career.'"
Broadway came next for the Yale English literature graduate, and after impressive performances in Tom Stoppard's Arcadia, David Hare's Racing Demon and The Iceman Cometh with Kevin Spacey, America's theatre business knew they were on to a serious talent. In fact, Giamatti was doing so well on stage that he never really applied himself to cracking the film industry. "I kind of looked upon it [films] as a cash machine while I did plays. I suppose the point at which that changed was a movie called Private Parts. It was certainly a bigger and better role than I had had before, and that was the point at which I started to get more film work than theatre work. I thought, `I'd better start taking this a little more seriously.'"
Despite several small but effervescent performances in pictures such as Donnie Brasco - where his "fuggedaboutit" dialogue with Johnny Depp steals the show - Giamatti never felt entirely comfortable with the medium. "I used to hate it. You just feel cut off from everything," he complains. "Cut off from your body, because it's just all about your face, and cut off from the other actors. It was OK when they were doing the master shot, but the minute they get in your face I still don't feel comfortable with that. I mean, who cares? There's something inherently sentimental about close-ups - it's all about your dewy eyes."
It seems almost incomprehensible that Giamatti, now a 37-year-old veteran of more than 30 films, including Saving Private Ryan, The Truman Show and The Negotiator, still feels ill-at-ease in front of a camera. Certainly, Giamatti still displays no warmth towards the artificial environment of filming. "I've learnt, or begun to understand, that the camera's the eye, and you know, that's the audience," he sighs. "You are actually performing for someone. There's someone the other side of the camera. And when there's someone to act with that's great because you forget about the whole damn thing."
Still, "the film stuff", as Giamatti repeatedly calls it, doesn't appear to be going too badly. "People in the industry and people like yourselves are saying that actors like me can flourish in this `new' environment, but I'm not convinced I believe them," he says. "I guess I'm just more cynical than that. There's no great paradigm shift in my opinion, and neither should there be. I just think I got really lucky."
Giamatti has found himself at the centre of a Hollywood scrum that will only increase if, as expected, Sideways wins an Oscar or two. "Honestly, I'm not being ridiculously self-deprecating here," he says, "but I'm delighted when we're nominated for these things... there's a kind of nameless, useless anxiety that accompanies being nominated, but I don't actually entertain the notion of us winning any of these things."
But if Sideways were to sweep to a Best Picture Oscar in a few weeks' time, what would be his dream project? "I loved working with Mike Newell on Donnie Brasco. And Alexander Payne on Sideways - he was great. He's got a literate and literary mind: he likes words, and I like words." And actors? "I've always admired Robert Duvall, so I'd get on the phone to him. Although what he'd want to do with me I do not know. And John Hurt - he's a great actor. So maybe all three of us get hooked up in some sort of crime caper. That sounds OK."
Having suggested that Flying Pigs might be a good working title, we get back to what the immediate future holds. For the moment, it seems, the balance of small parts in big pictures and leading parts in small pictures is set to continue. He has just finished a tiny independent film called The Hawk is Dying, which he describes as "an American Kes", and supports Russell Crowe in the summer-opening Jim Braddock biopic Cinderella Man. Perhaps more exciting for British audiences, though, is Giamatti's wish to join the Hollywood hordes in the West End. "I know Kevin Spacey a little," he schemes, "so maybe I could wheedle my way into The Old Vic."
For now we will have to be content with the quirky delights of Sideways - a film that has been called both redemptive and hopeful. Giamatti, however, disagrees: "I find it a very depressing movie," he says, as if he had nothing to do with the whole enterprise. "I mean, if that guy and that woman were to have a relationship, it's not going to be a very good one. He's an alcoholic and a wreck, and she drinks a little too much, too. And the marriage, don't get me started. That's going to be horrible. It's kind of a grim movie." This "grim movie" has floored entire audiences with its blend of tragedy and comedy. With Oscar night approaching, it looks like someone had better start writing that crime caper.