Start a conversation about Gaetano Donizetti's 1834 "Mary Stuart," which opened Saturday at the Ordway Center in a grandly sung production by the Minnesota Opera, and chances are you'll soon be talking about the blood-soaked patch of English history on which the work draws. Based on a play by Friedrich von Schiller, the opera seems overshadowed by its source materials, which librettist Giuseppe Bardari, a green 17-year-old, couldn't quite make his own. The result is a problematic hybrid -- "Masterpiece Theater" meets high-flying coloratura -- whose power stems more from the clash of its two queenly sopranos than from its theatrical (or musical) cogency.

That power peaks in the famous confrontation scene, invented by Schiller, which pits Elizabeth I against her cousin, Mary Stuart. The Earl of Leicester, loved by both women, has hatched a plan to free Mary, whom Elizabeth, a political rival, has long held captive. But Leicester's scheme goes horribly wrong, and with an imprudent outburst -- "Vile bastard," the opera's signature moment -- Mary seals her doom. One can imagine this encounter being played with greater melodramatic fervor than it was on Saturday, but not with more chilling elocution. (Alas, this pivotal scene comes rather early -- at the end of Act 1 in the company's two-act version of the score -- and leaves composer and librettist struggling to sustain dramatic tension thereafter.)

In Brenda Harris (Elizabeth) and Judith Howarth (Mary), Minnesota Opera has the two differentiated divas Donizetti demands. No one will confuse them. Harris, deservedly a company favorite, is an aging spitfire, regal even in her indecision -- she holds all the cards, and knows it. Her voice has an icy edge; her coloratura is a weapon. Howarth, though capable of a spine-awakening shriek, characteristically sings with melting lyricism. Her coloratura is laced with tenderness; she makes Mary's dubious transformation from charmer to martyr seem plausible. She's particularly affecting in her prayer, as is the splendid chorus (which is effectively deployed throughout this production).

Men are accessories in "Mary Stuart," but resonant ones. Bruce Sledge (Leicester) owns a fine Italianate tenor, though his acting can be stiff and his words indistinct. Jonathan Kimple (Talbot) is deeply sympathetic; Michael Nyby (Cecil), designedly, is not.

Kevin Newbury's staging, heavy with religious symbolism, will look familiar to veterans of last season's "Roberto Devereux," which ushered in the company's traversal of Donizetti's so-called "Tudor trilogy." D.M. Wood's lighting is especially striking. Conductor Anne Manson makes Donizetti's orchestration sound better than it has any right to; clarinetist Karrin Meffert-Nelson merits a solo bow.

Larry Fuchsberg writes frequently about music.