You'd probably think that "The Mexican," with stars as big as Julia Roberts and Brad Pitt heading the cast, would try to have them onscreen together as much as possible.

But this surprisingly edgy, risk-taking movie eschews such typical Hollywood thinking, and also turns quite a few conventions on their ears in the process. What may be the biggest gamble — and one of the most questionable in recent cinematic history — may be keeping its two superstars apart as long as possible (almost up until the final third of the movie, in fact).

But it's amazing how well that move pays off. In fact, almost everything works in this well-crafted dark comedy/thriller, which is easily the best, most enjoyable, major-studio-produced movie so far this year. (Be warned, however, that "The Mexican" is also quite violent and profane in places.)

Despite the fact that this may not be the weightiest of films, in terms of subject matter, it is also a little more observant — especially on the subject of relationships — than it might appear to be on the surface.

And let's not forget that it features two guaranteed box-office draws as its leads. The two stars play longtime lovers Jerry Welbach and Samantha Barzel, who are on the verge of breaking up.

For one thing, she's mad that Jerry is so selfish in their relationship. For another, she's annoyed with that her boyfriend is a small-time hood who seems to have no intention of leaving "the business."

Not that Samantha is perfect, either. Jerry's irritated at her continual harping, though he's hoping to settle into a more respectable life with her after he squares things with his rather shady bosses.

But things can't possibly be that easy for the couple. First, Jerry is sent to Mexico to pick up an antique (and supposedly cursed) pistol, and even when he does track it down, his rental car is stolen and he finds himself stranded, unable to communicate with the natives.

Meanwhile, an increasingly impatient Samantha has decided to make good on her promise to go to Las Vegas without him — until she's kidnapped by a soft-spoken hood (James Gandolfini, from cable television's "The Sopranos").

It's a fairly straightforward premise, but newcomer J.H. Wyman's screenplay is filled with all sorts of twists and turns, some very obvious and some that you'll never see coming.

But what may be the biggest surprise is that it's directed by Gore Verbinski, whose television commercial work and first feature, "Mouse Hunt," suggested that he was just another frantic, visually intensive filmmaker. His work here is much more subdued — he even allows his two leads to improvise. And again, when Pitt and Roberts are together, the film is positively electric. In fact, Pitt's loose, limber performance goes his "Snatch" work one better.

However, the charming-as-usual Roberts may have even better chemistry with slimmed-down co-star Gandolfini, who manages to send up his usual tough-guy characters.

And if that wasn't enough, there's also a winning harmonica-and-banjo score (by Alan Silvestri) and an amusing and unbilled celebrity cameo that is neither out of place nor distracting.

"The Mexican" is rated R for strong violence (mostly gunplay and a brief pummeling), frequent strong profanity, gore and some crude sexual talk and use of sexual slang terms. Running time: 123 minutes.

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