After exuding clever charm and dodging most of the cheap Cinderella contrivances that linger around every corner of its plot, the ostensibly crisp romantic comedy "Maid in Manhattan" turns so unforgivably trite in its last 10 minutes that any moviegoer without a fortified sweet tooth will likely be sent into sugar shock.

Provided with more depth than most genre heroines, star Jennifer Lopez shines brightly as Marisa Ventura, a single mom from the Bronx who works as a maid at one of New York's most posh hotels. Mistaken for a ritzy guest while trying on a $5,000 Dolce & Gabbana suit in someone's luggage, she catches the eye of Christopher Marshall (Ralph Fiennes), the flirtatious and good-looking heir to a political dynasty, and quickly becomes the object of his affection -- and of much speculation in the New York tabloids during Marshall's run for congress.

Trapped into maintaining the illusion for the time being, Marisa ends up risking her shot for a management position as real life starts catching up with her. But in the hands of discriminating director Wayne Wang (who brings emotional authenticity to both independent films like "Center of the World," and studio pictures like "Anywhere But Here"), this fairy tale is refreshingly substantial fare with quality, character-building and considerably less predictability than recent dumbed-down hits like "Sweet Home Alabama." Or so it seems for a while.

Marisa does not spill anything on the expensive white suit. She doesn't have a nefarious boss or any backstabbing co-workers (although a snooty guest played by Natasha Richardson is quite grating). She does have something more than romance on her mind ("Maybe you should spend some real time in the projects instead of making up speeches about them," she spontaneously scolds Marshall on a date). She has a strong relationship with her 10-year-old son (Tyler Posey), who takes a shine to Marshall, and vice versa. And she ends up facing some real-life (not cartoonishly scripted) consequences of her actions.

Of course, Marisa also gets swept off her feet and attends a fancy fundraiser in a knockout gown (floor-length, strapless pink chiffon on loan from a friendly store in the hotel lobby) that leaves the handsome candidate, all his cronies and most of the movie's audience utterly agog.

But the fact that Fiennes' off-the-shelf Prince Charming is also a very vanilla politician (an "environmentalist Republican" more concerned with love than his campaign image) is the movie's first sign of trouble, since we're left to wonder what it is about the guy that makes Marisa fall for him.

This lukewarm chemistry doesn't stop Lopez from selling that love anyway in a terrific, intelligent, sincere and buoyant Everygirl performance that draws on her own downtown roots for veracity. One person with whom she does have great chemistry is the kid playing her son. Their mother-child interaction certainly helps bring the film into the third dimension.

Yet for all the efforts of Wang and Lopez to rise above the inherent froth of the Cinderella storyline, "Maid in Manhattan" tanks after the inevitable reveal of the truth about Marisa's current station in life. The film succumbs to the insipid notion of an absurdly public reconciliation and declaration of love in front of a surrogate audience (think "Notting Hill"), which is placed in the scene specifically to tell us when to clap and when to "awww!"

This is something no movie should need or want if it's done its job of engaging the real audience's emotions. "Maid" does engage quite well, in spite of its flaws, right up to the point where the ingenuous Wang inexplicably gives up and puts the picture on autopilot.

The fact that "Maid in Manhattan" does, for 90 or so of its 103 minutes, seem both sweet and refreshingly genuine is almost a miracle anyway -- especially since it has to fight the original script by John Hughes (the "Home Alone" movies) and a score of 200-proof saccharine (by the prolific Alan Silvestri) with all the sophistication of a 1950s Disney children's matinee.

It's just a shame that miracle couldn't hold out.