Daphne Rubin-Vega is the chief reason to see Emily Mann’s beautifully staged but uneven revival of the Tennessee Williams classic The Night of Iguana, which opened Sunday at Off Broadway’s Pershing Signature Square. The two-time Tony winner, best known for her work in musicals, here embodies one of Williams’s most intriguing female characters: Maxine Faulk, a widow of two weeks who throws herself at the defrocked Episcopal priest turned tour guide, Lawrence Shannon, who’s been a regular visitor at the Mexican beachside resort that she’s now running solo. Here is a middle-aged woman in 1938 who is aware of her body, unafraid of flashing her still-impressive decolletage, and who is willing to embrace her sexuality even as she recognizes the limits of her chosen paramour (played here by the all-too-likable Tim Daly).

In Rubin-Vega’s hands, Maxine is both lusty and savvy, delivering her lines with a throaty all-knowingness that makes her instantly recognizable and sympathetic. The other standout here is Austin Pendleton as the doddering, nearly destitute nonagenarian poet who turns up at the resort with his granddaughter (Jean Lichty), an artist manquée who is struggling to keep them both afloat financially. Lea DeLaria also makes a striking impression as a “butch” Texas Lutheran who’s part of Shannon’s latest tour — which goes off the rails after he seduces one of its 16-year-old members.

Alas, the central couple seem less comfortable in their roles. Daly portrays a cipher of a man on the verge of what we’re told is another crack-up, but he seems so calm that he’s almost sleepwalking through a personal and professional crisis of his own making. Meanwhile, Lichty, as a spinster nearing 40 who sees in Shannon an unlikely kindred spirit and perhaps romantic opportunity, seems alternately too tentative and too bold.

Worse, Mann treats most of the play’s minor characters as comic-relief throwaways, from Maxine’s young Mexican workers to the German couple that is staying at the resort and celebrating the Nazis’ late-1930s victories overseas. They seem out of place in a drama that otherwise wants to ground us in a very human reality.

Still, there’s no denying the poetry of Williams’s language. And the physical production is impressive — from Beowulf Boritt’s spare set to Jeff Croiter’s subtle lighting to Darron L. West’s tropical sound design. This is a languidly paced drama that still holds some real power — never more so than we see Rubin-Vega’s face and the depths that it shows, including those just beneath the surface.