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Sanaa Lathan is as tough as she is fetching, which is why it’s so disheartening to watch her play a dopey victim for much of “The Perfect Guy,” in which her well-to-do professional is terrorized by a new flame who doesn’t take kindly to being dumped. Boasting a screenplay by Tyger Williams that never fails to telegraph its every move, David M. Rosenthal’s film is a cheap “Fatal Attraction” knockoff, complete with a subplot involving the potentially dire fate of Lathan’s beloved pet. While no bunnies wind up being boiled, the rest of this second-rate genre effort is a strictly by-the-books affair. Despite an appealing trio of leads, it seems likely to entice only those with an unquenchable thirst for thriller cliches.

Leah (Lathan) is a successful California lobbyist whose relationship with Dave (Morris Chestnut) falls apart due to his disinterest in committing to the type of marriage-with-children future that she craves. No sooner has she dropped Dave than Leah is swept off her feet by Carter (Michael Ealy), a sexy suitor who first meets her at a coffee shop and, following another chance encounter that ends with her literally swooning over his kisses, reveals himself to be everything — devoted, passionate, respectful and interested in starting a family — that Leah wants in a partner. In case that wasn’t immediately clear from Ealy’s perpetually humble-and-sweet routine (not to mention the film’s title), Leah’s friend Alicia (Rutina Wesley) bluntly states, “He might be the perfect guy!” — thereby cementing the filmmakers’ dedication to making everything about their story as leadenly obvious as possible.

After a weekend at her parents’ house, during which Leah’s new beau wins over her dad (Charles S. Dutton) with front-row San Francisco Giants tickets, Carter loses his cool at a gas station and viciously beats a man he mistakenly thinks is hitting on Leah. That violent outburst so rightfully frightens Leah that it ends their relationship, and Carter takes the development quite badly. As an IT expert with all sorts of stalker-ish skills involving security systems and spy cameras, Carter quickly becomes a menacing thorn in Leah’s side, especially once she reconciles with Dave. His attempts to make Carter stay away from Leah via public threats are as useless as the detectives looking into Carter’s behavior, and the restraining order Leah eventually gets against him.

As Ealy’s conduct tips over into lunatic territory, director Rosenthal recasts him as not only an unhinged ex, but a psychotic in a distinctly horror-movie mold. Standing in a doorway looking down on one of his victims, Carter assumes a stoic Michael Myers pose. Later, his surreptitious appearance outside Leah’s shower — in which she’s canoodling with Dave — turns him into a Norman Bates-ish madman. Meanwhile, Dave is rendered as such a trivial would-be protector that his powerlessness practically oozes off the screen (this despite obligatory shots of a shirtless Chestnut’s buff body), and Leah is forced to assume the role of helpless prey, incapable of enlisting the help she needs, or attaining the necessary strength herself, to stop her former boyfriend from destroying her personal and professional lives.

Eventually, Williams’ script has Leah turn the tables on her tormentor, thereby finally allowing Lathan to exhibit the gritty ferocity — as demonstrated in films including “Blade” and “AVP: Alien vs. Predator” — that makes the accomplished actress more than just a pretty face. Unfortunately, it’s far too little too late to salvage “The Perfect Guy” from its own dull suspense. It may be awash in Internet-age fears about surveillance and identity, but at heart, it’s little more than a retrograde B-movie.

“The Perfect Guy” — Two stars

MPAA rating: PG-13 (for violence, menace, sexuality and brief strong language)

Running time: 1:40

Opened Friday