Hardened operagoers might be understandably apt to assume Rossini's Tancredi is a musty curio full of gods and monsters, warbling at length with interchangeable personalities. Rossini operas can be like that.

Yet the first half hour of Opera Philadelphia's opening of Tancredi, which runs through Sunday at the Academy of Music, no doubt made such notions evaporate, even in an initially tentative performance with a cast full of fine singers all new to their high-wire roles.

Mezzo-soprano Stephanie Blythe was the big name, and she took a while to settle in as the disgraced warrior Tancredi, though soprano Brenda Rae -- a discovery for many -- became a constant source of vocal allure with the kind of dramatic instincts that turn a flashy cadenza into an intense character study. Michele Angelini's soft-grained tenor isn't yet fully grown, though his Act II soliloquies made you happy not to have a less-sensitive powerhouse voice. Baritone Daniel Mobbs required no warm-up: He's one of the few singers out there whose physical and vocal gestures are all of a piece.

That's the starting point of any good Rossini production, and after intermission, performances mostly hit that ideal bel canto nexus of exciting vocal risk without calculation. Only beyond that does one start noticing that Tancredi, written early in Rossini's high-velocity career, has far more to say than his supposedly more evolved voice fests, like La Donna del Lago. Even when Blythe, for one, didn't nail an aria, her dramatic intelligence plus the richness of her voice (especially her arresting low notes) meant recitatives were as important as anything else in the opera.

All such factors conspired to make Tancredi -- with its story of star-crossed love between Tancredi and a noblewoman wrongly accused of treason -- more than an opera, but a parable of timeless archetypes. That's partly because Rossini took the story seriously. And so did the production.

Though Opera Philadelphia doesn't have a consistent history of succeeding with big-house risks (remember that Romeo et Juliette production?), the current Tancredi has handsome, neoclassic sets by Daniel Bianco that update the action to a more familiar, post-World War I era of societal sea change. The combination of Emilio Sagi's sensible, voice-projection-friendly stage direction and conductor Corrado Rovaris' lively but flexible tempos created a solid framework that could buoy weaker moments. Even when tenor Angelini was concentrating far more on notes than meaning, Rovaris told you everything you needed to know.

The quiet ending that concludes the opera couldn't have been trickier, since it's grand opera that needs to have the intense intimacy of a song recital. Together, Blythe and Rovaris created subtle moments that showed. No matter how unorthodox the ending, it spoke more clearly than any fortissimo. The super-quiet Friday audience seemed mesmerized -- a quiet triumph, indeed.

Performances of Tancredi are Wednesday, Friday, and Sunday at the Academy of Music. Information: 215-732-8400 or www.operaphila.org.