Still, she got to the core of the character, especially in the confession scene, one of the most inspired in the opera. Adalgisa comes to Norma’s home, which here looks like some gargantuan forest igloo made of branches and sticks, to confess that she has broken her vow of chastity and fallen in love. At first, Norma is motherly and understanding. After all, though she keeps this to herself, she’s been there.

The tenor Joseph Calleja is Pollione, the Roman proconsul and Norma’s lover who, we soon learn, has now fallen for Adalgisa. Though Mr. Calleja’s voice is by nature burnished and ardent, he has a tendency to sing with a slightly nasal quality that can result in a pinched tone. That was a problem here.

Also, perhaps with Mr. McVicar’s encouragement, Mr. Calleja played Pollione, at least initially, as entitled and self-absorbed, and seemed uncomfortable doing so. There was a telling moment when Norma erupts, furious and humiliated to discover her lover’s betrayal. This Pollione rubs it in: Mr. Calleja, lifting Ms. Radvanovsky’s chin in his hand, almost mocked her as he confirmed the worst.

Whatever these frustrations with Mr. McVicar’s staging, the greatness of the opera came through in scene after scene. In Act II, Norma, half-crazed with despair, approaches her sleeping boys with the intention of killing them, rather than letting Pollione scurry them off to Rome. Ms. Radvanovsky brought tremulous poignancy to these aching phrases.

The long, complex scene when Norma and Adalgisa work through their crisis and discover sisterly friendship was, as it should be, the highlight of the evening. Whether trading soaring lines or joyously skipping up the scale in perfectly synchronized thirds, Ms. Radvanovsky and Ms. DiDonato brought out the best in one another.