B-

The idea of a son who tries to break up a possible romance for his single mom is hardly a new comedic premise—does anybody remember Jason Bateman’s short-lived mid-nineties sitcom “It’s Your Move”?—but it’s given unnerving, if often bleakly funny, treatment in the Duplass brothers’ “Cyrus.” You might call it the anti-Hollywood Hollywood romantic comedy, naturalistic and acerbic rather than slick and saccharine.

John C. Reilly stars as John, a pathetic, divorced editor with a disastrous social life. One night at a party to which he’s dragged by his concerned ex Jamie (Catherine Keener) and her fiance Tim (Matt Walsh), he meets Molly (Marisa Tomei), with whom he hits it off immediately, even though he’s drunk and more than a mite boorish. But she’s secretive, slipping out of his apartment early after spending the night (something she repeats on further occasions). He begins to suspect she might be married, but by following her one night he discovers the reason—she has a grown son named Cyrus (Jonah Hill), whom she’s brought up alone and home-schooled, and mother and son dote on one another.

Initially Cyrus, a stay-at-home wannabe musician, seems to welcome John into the family equation. But it turns out that’s just a pose. Behind the accommodating façade he tries subtly to sabotage his mother’s new relationship in order to maintain his own somewhat creepy one with her. John suspects what he’s up to, but Molly’s oblivious to what’s going on, and the upshot includes romantic setbacks, breakups of various sorts, confrontations and reconciliations. There’s some sweetness here, but more oddity and even a hint of danger.

Just as the picture avoid the usual conventions of plot, so do the Duplass brothers avoid those of style. Following the practices they followed in their earlier low-budget pictures, they use improvisation, long takes and hand-held camera work to give the scenes a sense of immediacy and gritty authenticity unlike what’s commonplace in ordinary Hollywood fare. The result is a movie that will strike many viewers as ragged and even technically oppressive (the zooms into close-up of the characters’ faces aren’t pretty), but it’s part of the technique.

And the cast seem to have taken well to the approach. Reilly’s grubby everyman persona fits the sad-sack, lovesick protagonist perfectly; despite having to do some rather unpleasant things, he manages to be sympathetic, and is convincing as a guy who might be a bit slow but isn’t dense. Hill tunes back his customary over-the-top ebullience to deliver a turn marked—except during Cyrus’ occasional explosions—by a cool, unnerving restraint, cannily fashioning a credible portrait of a young man who’s mature on the outside but still childlike and socially inept on the inside. (Together with his recent performance in “Get Him to the Greek,” Hill is showing real range.) It’s the chemistry between these two that sells “Cyrus,” but Tomei is also excellent as the conflicted Molly, and Keener does her usual solid work as John’s concerned ex.

With its rather primitive appearance—some of the picture actually looks like an amateur effort—and its decidedly skewed take on relationships, “Cyrus” isn’t going to satisfy viewers searching for the next Judd Apatow laugh-fest. This is much more character-oriented comedy-drama, and the tone is far less broad. But as the first studio effort from the Duplass pair, it shows the brothers’ courage in trying to maintain their distinctive sensibility on a larger canvas. The result isn’t perfect, but it’s far more interesting than the cookie-cutter junk that passes for Hollywood romantic comedy nowadays.