Both old-fashioned and modern, funny and melancholic, the witty, heartfelt Celeste and Jesse Forever is populated by moments that at first appear all too familiar, then turn out to surprise you.

This more-than-welcome pattern begins early in the movie, when Celeste (Rashida Jones, in a career-altering performance) and Jesse (Andy Samberg, every bit as good) share a disgustingly cute conversation, accents and all, with their soon-to-be-married friends, Beth and Tucker. Out of nowhere, Beth has a fit, not because out of the cutesy behavior itself, but because such behavior is entirely inappropriate for a couple like Celeste and Jesse — who are about to be divorced.

Therein lies the highly original, yet entirely plausible premise of the film: a couple that is doing everything (and I mean everything) in their power to remain best friends forever, even when it seems that their partnership is coming to an inevitable end. Even when their affections are unequal and keep changing.

At the center of this spectacle is Celeste, a controlling career woman who has given up on Jesse, a slacker whose greatest ambition seems to be watching reruns of the 2008 Olympics, as husband material. We've seen people like this on the screen many times, but Jones and Samberg play off each other beautifully and imbue these folks with warmth, depth and vulnerability — without compromising their characters. We like them, and they make us believe they share a unique friendship, even if it's emotionally immature at times.

Jones and Will McCormack (hilarious as Celeste's pot dealer friend Skillz) co-wrote the script, which offers plenty of offbeat supporting characters: Elijah Wood has a nice turn as Celeste's un-hip gay co-worker; Emma Roberts has fun as Celeste's troublesome but observant pop star client; and Chris Messina is appealing as a roguish yoga student/pickup artist.

Director Lee Toland Krieger not only gets winning performances from his entire cast but creates a Los Angeles that for a change actually seems like Los Angeles.

One could quibble that the film is self-consciously clever at times, and the project, influenced by When Harry Met Sally ..., could jokingly be called When Celeste Divorced Jesse ... . But this film has a voice of its own. And at a time when the romantic comedy seems to be a lost art form, that's saying something.