For a symphonic ensemble that is never in the orchestra pit, playing operatic repertoire means an exciting exploration of new music: on Saturday night, in the Koussevitzky Shed at Tanglewood, the Boston Symphony Orchestra played Puccini’s La bohème complete for the first time! Under the baton of Andris Nelsons – who happens to be one of today’s great opera conductors without having been affiliated with opera houses since his youthful days in Latvia – the BSO was in top form.

Led by First Associate Concertmaster Tamara Smirnova, the BSO played with an enthusiasm that members of a pit ensemble, playing season after season multiple renditions of this extremely popular story of love and poverty, would have difficulty summoning. Under Nelson’s watchful eye, the orchestra offered an extraordinary support for the singers, never overwhelming the voices. The musical canvas was remarkably supple, with proper light shed on Puccini’s melodic inventiveness and wondrous orchestration.

The performance, announced as semi-staged, involved a lot of moving around (at different points, members of the excellent Tanglewood Festival Chorus and a small band were meandering between the stalls) and a multitude of scenographic props (from a free-standing stove and raffia baskets with food and bottles of wine to small restaurant tables and the unmissable Récamier sofa which acts as Mimì's deathbed). The overcrowding of the stage was at no point of Zeffirellian scale, but director Daniel Rigazzi did an excellent and compelling job.

Mimì is one of Kristine Opolais’ roles in which she can display not only her vocal charms, her fluid sound and dark inflections, but also her obvious acting talent, conveying Mimi’s mixture of shyness and sensuality. She started tentatively, but grew in assurance. Rodolfo was supposed to be sung by a specialist in this role – Piotr Beczała – but, in a not so uncommon game of musical chairs, the Polish tenor stepped in at short notice to save Bayreuth's new production of Lohengrin. Beczała's replacement, Jonathan Tetelman, has the looks and enthusiasm to play Rodolfo. He succeeded less in portraying the young poet becoming emotionally mature upon being confronted with the illness and death of someone he truly loves. Tetelman doesn’t possess the largest of voices and can sound strained in the upper register. “O soave fanciulla” was muffled by a rapidly passing storm, but later Mimì/ Rodolfo duets demonstrated a good chemistry between the two protagonists. During “Sono andati?”, Opolais' voice faded with exquisite naturalness.

Susanna Phillips has sung Musetta often. It’s amazing how she can still muster the will to uncover new facets of this character: playful and coquettish in her opening waltz “Quando me’n vo”, subdued, introspective and full of tenderness in the closing prayer, feisty and self-assured in between. Musetta’s on–off lover, the painter Marcello, was interpreted by baritone Franco Vassallo with beautiful legato. He was the true binding factor for the entire cast of characters.

Philosopher Colline sings only one significant aria (“Vecchia zimarra”, an ode to his old coat). The great bass-baritone Luca Pisaroni dispatched it with elegance and assurance, making one wish Puccini had elaborated the role more. As Schaunard, the fourth in the quartet of Parisian friends, baritone Elliot Madore was hyperactive and full of smiles. In the double roles of Benoît and Alcindoro the semi-retired, veteran bass Paul Plishka had difficulties projecting his voice but succeeded in rendering the characters’ ridiculousness. Tenor Neal Ferreira made himself noticeable in the smallish role of the street vendor Parpignol.

Andris Nelsons and the BSO should pursue exploring the operatic repertoire for the benefit of both musicians and their enthusiastic public. There are many masterpieces that don’t really lose much of their impact and expressive power in the absence of a full staging.