In the clay-floored confines of the Koussevitzky Shed the BSO brought together a collection of suitable vocal forces for Saturday’s semi-staged Tosca. The Italianate tenor SeokJong Baek transmitted powerful waves of reckless, youthful vigor of the painter Cavaradossi. Bryn Terfel shone the lustful menace of the villain Scarpia. Kristine Opolais elicited strong sympathy as the anguished Floria Tosca. The contrast between her rather tentative forte high notes and her excellent control of the lyrical mid-range proved emotionally engaging.

Puccini had been famously obsessed with faithfully embedding textures of real soundscape of Rome into the premiere of this conflict-laden story. He made a special effort to match the tone of St. Peter’s bells into the sequence leading up to the Te Deum procession and the morning chimes of multiple churches into Act 3. The Eternal City had been given a part in the production, but the peaceful night in Lenox provided little noise to match that expectation. Instead, the part of an actively participating external world landed with the BSO, and the orchestra turned into a critical participant in the drama — something you can’t automatically count on in a theater in which players hide in the pit, while voices comfortably project beyond the footlights and steal the show.

Individual sections delivered critical support and rendered vocal parts more robust and credible. The First violins supported the lyricism of Floria and Mario’s duet in the first act, while the soprano and the tenor negotiated the dynamic range. Blaise Désjardin’s cello doubled the emotional impact of Tosca’s lamentation on unrewarded virtue in the second act, and in the third act, returned with the same leitmotif to a comparable effect. The cellos’ playing in the upper range, with both power and tension, also drove the build up to the climax of the opera, Mario’s E lucevan le stelle. And William Hudgins’s clarinet solo of that theme, in its slow and contemplative glory, nearly stole the thunder of the aria.

But above and beyond these solo episodes, Andris Nelsons steered the ebb and flow of the orchestra into magical realms. The first taste came with the Te Deum at the end of Act 1, as he built up a veritable tsunami instrumental tutti with the glorious Tanglewood Festival Chorus. [And attention should be paid to Heinrich Christensen’s ministrations on the Shed’s rarely heard Æolian Skinner. Few operhouses nowadays can achieve the effect.]The broad tempi and fluid phrasing of orchestral answer to Tosca’s aria in Act 2 fully restored the tension of the narrative line, which was no small feat, given the traditional enthusiastic uproar of the audience in reaction to that aria, which Opolais delivered with splendor.

Speaking of the operatic conventions, Bryn Terfel’s theatrical talent contributed almost as much as his masterfully modulated voice. At the end of audience clapping, after a dramatic pause, he added some mocking applause of his own, rounding off a well-crafted image of a tyrant who, at least for a moment, enjoys full control of all mechanisms of power.

Some other elements of stage craft seemed more distracting than enhancing the story line: the chef’s knife that was destined to dispatch the bad guy seemed far too large to hide and to wield, and the long and inaudible guns of the firing squad added little in the way of credibility. But all in all, the efforts to implement some stage business helped, with many little elements contributing in their independent way. Morris Robinson’s Angelotti persuasively stumbled onto stage to kick off the action, and Neal Ferreira’s Spoletta in his sharply tailored suit channeled an intimidating mob enforcer in the subsequent scene of Act 1. Whatever Terfel sipped from two different wine glasses on two different tables only enhanced the venomous power of his character and the confidence of his voice projection.

In the third Act, the orchestra ruled again. The pastoral beginning, much enhanced by puerile charm of Ari Davis’s Shepherd Boy, unraveled with tectonic power. Baek’s aria excited the audience to the hilt. Tosca’s final jump made as much of a mark as could be expected on a semistage: she ascended to the center-back of the orchestra and shone for a brief moment against a bloody backdrop of a Roman sunrise, disappearing into the darkness. Still, with all those theatrical pleasures, it was the languidly churning swells of the orchestra that most heartened us.

Victor Khatutsky has written for the Intelligencer since 2014. He also interests himself in genomics and the poetry of Boris Pasternak.