Despite some bumpy tonal shifts and inconsistencies of characterization, “Hello, My Name Is Doris” impresses as a humanely amusing and occasionally poignant dramedy about a spinsterish office drone who develops a romantic fixation on a much younger co-worker. The plot could have been played as a flat-out broad comedy or an anxiety-inducing psychological drama, and there are times when it feels like helmer Michael Showalter is striving for a mash-up of both. But Sally Field keeps the movie on an even keel, for the most part, with an adroit and disciplined lead performance that generates both laughter and sympathy, with relatively few yanks on the heartstrings. Audiences of a certain age might respond warmly, provided they are stoked by savvy marketing and favorable word of mouth.

Anyone who has ever toiled in a honeycomb of office cubicles will recognize Doris Miller (Field), the sort of hard-working but good-natured sixtysomething whose after-hours life remains a mystery that few co-workers investigate, or even imagine. After decades of caring for her aged mother in their cluttered Staten Island home, a place that could have been showcased in an episode of “Hoarders,” Doris is hard-pressed to find a new purpose in life after her mom’s demise. Inspiration is where you find it: When she attends a lecture by a motivational guru (Peter Gallagher), Doris is unexpectedly receptive to his smooth talk about taking big risks and pursuing fresh goals.

Enter John Fremont (Max Greenfield), a hunky young design executive newly transferred from Malibu to Doris’ Manhattan workplace. Doris is smitten, but too timid — and, perhaps, too inexperienced — to make an effective bid for his attention. She needs some help from the precocious teen granddaughter (Isabella Acres) of her brassy best friend (Tyne Daly) to devise a game plan that includes some Facebook deception, a strategic indication of share interests, and a “chance” meeting during a club appearance by John’s favorite electronica band.

Working from a screenplay he and co-scripter Laura Terruso adapted Terruso’s short film “Doris & the Intern,” Showalter doesn’t always make it clear during the early scenes whether we’re supposed to be laughing at or with his lovestruck protagonist. When Doris is accepted by John, other young people at the club and the band’s lead singer as a kindred spirit, the gag appears to be building toward a hilarious payoff. But then the movie goes one step beyond — Doris is recruited to pose for the cover of the band’s next album, cuing an aggressively wacky photo shoot — and viewers can’t help wondering whether Doris is being treated as an eccentric mascot or, worse, a cliched silly senior citizen.

The mood swings accumulate as the plot proceeds apace. When Doris discovers that John actually has an age-appropriate girlfriend (Beth Behrs), she impulsively sabotages their relationship in a move that seems to signal a detour into darker drama. That impression is only increased at the two-thirds point as Doris — who , in true hoarder fashion, refuses to part with the piles of junk cluttering her home — angrily uncorks long-simmering resentments while responding to an intervention by Todd (Stephen Root), her concerned brother, and Cynthia (Wendi McLendon-Covey), his unpleasant wife.

Doris’ jolting explosion is, quite literally, a showstopper — arguably the only moment in the movie that acknowledges what she sacrificed to be a dutiful daughter — and Field plays it for all its worth. The scene has such potent impact, however, that Field, Showalter, Terruso and practically everyone else involved with “Hello, My Name is Doris” must work doubly hard to coax us into believing, or at least accepting, a relatively happy ending.

It helps a lot that Field remains winning, even while Doris edges toward extremes. And it helps even more that, while the filmmakers stop far short of transforming Doris with a glam-fab makeover, Field never appears so dowdy that credibility becomes a major issue. (If she were that dowdy, this would be quite a different movie.) To put it another way: The Oscar-winning actress looks and acts her age — except, of course, when Doris goes clubbing — but it’s not that hard to believe that maybe, just maybe, her character might captivate the object of her desire.

Greenfield plays John with just the right balance of mixed signals, so that we, like Doris, aren’t always certain about his true feelings in regard to his older co-worker. Daly manages a similarly tricky juggling act as Roz, Doris’ outspoken Old Leftie friend, who likely would do well to pursue some fresh goals of her own. Among the other supporting players, Root makes the most of an underwritten role, subtly suggesting that Todd is being less than honest when he insists he and his sister mutually agreed long ago that Doris, not he, should be their mother’s caregiver.

Production values, including the electronica music, are fine.