Tony Scott loves Mexico City. The ''Spy Game'' director's new movie stars Denzel Washington as a combustible mercenary who takes a gig protecting Dakota Fanning from Mexican kidnappers, and Scott shot the whole movie there. ''It's tough, it's dirty, it's dark, it's SEXUAL,'' he purrs. ''It's a real wild place, and you can feel that tension on the streets. I think it serves our movie well.'' It served, at least, to bond the costars. ''One time we were filming on this street and it smelled SO BAD,'' says Fanning. ''Denzel and I were joking about it.'' The two-time Oscar winner quizzed the 9-year-old ''Cat in the Hat'' pint-sizer on her state capitals between takes, but don't hold out for a happy, fuzzy Denzel on screen. ''He's out there in this one, taking huge risks as an actor in the second half,'' says Scott, who was rejected as director of the project ages ago (it was then mangled into a 1987 turkey of the same name starring Scott Glenn). But Scott feels good about his remake. ''It's not 'Death Wish','' he says. ''It's the biggest, edgiest movie I've ever done, and it's a huge emotional roller coaster.''