The premise of Mozart’s “Cosi fan tutte” is simple:

Two men, Ferrando and Guglielmo, try to prove to their older, pessimistic friend that their fiancés are faithful to them. Don Alfonso rejects the notion that any woman could be faithful – no offense to the sisters Dorabella and Fiordiligi – so he puts the quartet to the test. He sends the officers off to “war,” and they return minutes later disguised as exotic foreigners, tasked with seducing the women.

The twist is that the officers don’t woo their own betrothed, but rather their friend’s: Fiordiligi falls for Ferrando, and Dorabella for Guglielmo.

A simple premise, indeed, but one full of awkward psychological implications for the characters. Can the lovers reconcile once the trick is revealed, as inevitably it will be? If, as the Italian title suggests, “all women, they do so,” then aren’t the men equally at fault for tempting their best friend’s lover – and for deceiving their own fiancés?

Interpreters of Mozart’s music and Lorenzo Da Ponte’s libretto must convey these inherent tensions, which fluctuate between the comic and the tragic. Pittsburgh Opera’s “Cosi fan tutte,” which opened Saturday night at the Benedum Center, embraced the multifaceted character of the opera in a pared-down production that plumbed much of the opera’s depth. The estimable British baritone Sir Thomas Allen, who also portrayed Don Alfonso, directed the production.

Much of the tragedy in this staging was singularly rendered by Danielle Pastin, who depicted Fiordiligi. The most complex character in the opera, Fiordiligi is torn up about betraying her fiancé, where her sister is somewhat flighty on the matter.

At first, this representation was necessarily one-dimensional: Fiordiligi followed the expectations she had for herself, and that others had for her. But Ms. Pastin revealed the character’s internal battles throughout the opera, particularly in the second-act rondo “Per pieta.”

The soprano painted those interior emotions with a lively, expressive timbre, a natural music line and an even tone that supported her imaginative phrasing and stunning dynamic contrast. So tortured was this characterization that, by the end, one hoped she would end up with Ferrando, with whom she was more infatuated than the virile Guglielmo.

As Ferrando, tenor Christopher Tiesi had an appealing, sweet timbre but did not match that emotional dimensionality. He struggled with the role’s highest notes and relied on vibrato where other expressive tools were needed.

Mr. Allen, in his Pittsburgh Opera debut, carried himself with the sturdy confidence of Don Alfonso and also served as a thoughtful director. During the Act I quintet, right before the young officers departed, teary-eyed, for their regiment, Don Alfonso mocked the lovers from the other side of the stage, reminding the audience that the whole thing was a sham. Most effective was his creative staging of the finale: He replaced Mozart’s design, in which the original pairs reconcile, with a scenario that seemed better suited for this production. Still, the spare scenery designed by John Conklin looked too small for the Benedum stage.

In a comic delivery of Dorabella, former resident artist Jennifer Holloway offered a full, round tone, particularly in the upper register. Hadleigh Adams captured Guglielmo’s machismo with a gravelly, dark-hued timbre. As Despina, Sari Gruber gave amusing takes on the maid’s disguises, even if her voice could be tight in other moments.

Music director Antony Walker conducted the lithe orchestra, with the continuo played on an upright piano.

First Published: November 8, 2015, 8:57 p.m.