‘Tosca’ Is the Boston Symphony’s Andris Nelsons at His Best

Andris Nelsons may have become a fitful, inconsistent music director of the Boston Symphony Orchestra, but every once in a while, he proves that he has still got it.

Such was the lesson on Saturday night at Tanglewood, the Boston Symphony Orchestra’s summer home in the Berkshires, as Nelsons and a starry cast delivered a concert “Tosca” of high intensity and even higher emotion.

This Tanglewood season is a solid one, with the premiere of a new John Williams piano concerto written for Emanuel Ax on the agenda next weekend, a Gabriela Ortiz-curated Festival of Contemporary Music sprawling around the grounds at the same time, and the obligatory appearances of Yo-Yo Ma, famous friend of the orchestra, to come in August. New at Tanglewood this year: tastefully installed screens next to the Shed stage that show the musicians at work, and, by some miracle, enhanced cellphone service. Still unchanged: the humidity.

But “Tosca” was always likely to be a high point of the season, and it was. Opera has often brought out the best in Nelsons in Boston, and the closer to the most commonplace parts of the repertoire the work has been, the stronger the performance from him. Wagner transfixed him as a child, and it was at the Latvian National Opera that his career began to take off in his 20s. Now 46, he rarely looks more engaged on the podium than when he is supporting a singer in full flow.

And for this Puccini, Nelsons had some singers of quality to support. Bryn Terfel sang his last staged Scarpia at the Met earlier this year, but he still brings unrivaled authority and conviction to a role that has defined his career. Has the passing of time brought a more vicious edge of desperation to his portrayal, as if an older Scarpia might feel as though this is his last, appalling chance to corner his prey, causing him to act with such depravity? Either way, Terfel’s snarling chief of the Roman police remains a privilege to see.

So, too, the glorious Cavaradossi of the Korean baritone-turned-tenor SeokJong Baek. Here, as at the Met last fall, his extraordinarily firm, high cries of “Vittoria!” drew instant applause, and they were far from the only point at which this colossal voice, wielded by turns with machined precision and melting sensitivity, could have earned such approval.