NEW YORK — The unofficial Yannick Nézet-Séguin festival at Carnegie Hall opened Monday with the first of three concerts over two weeks that include a Philadelphia Orchestra appearance on Friday, but otherwise showcase the Met Orchestra in its annual spring emergence from the Metropolitan Opera pit and onto the Carnegie stage.

Programming for Monday’s Met Orchestra was typically unstartling: The idea is to bring fresh responses to oft-heard symphonic repertoire that regular symphony orchestras take for granted, though often with a wild card.

With Nézet-Séguin, just back from the Philadelphia Orchestra’s China tour, that concept fell pleasingly into place with Debussy’s La Mer and Ravel’s Daphnis et Chloe Suite No. 2, plus mezzo-soprano Isabel Leonard singing Ravel’s Sheherazade — and then Henri Dutilleux’s still-fledgling 2009 Le Temps l’horloge (Time and the Clock).

Performances were sometimes undercooked, but with plenty of compensation. I would want to be there if only for Dutilleux's song cycle, heard for the first time at Carnegie Hall in its full version.

The composer (1916-2013) worked slowly and fastidiously, always staking out new ground and never more so than in this late-period work. Then in his 90s, he idiosyncratically augmented the orchestra with harpsichord and accordion to deliver sounds even a master colorist like him hadn’t explored.

No, this isn’t some elegiac swan song, but a compact, occasionally spoken treatment of poems that attack the concept of time from various perspectives, ending with Baudelaire recommending that we all just get drunk so as not to be “martyred slaves of time.”

Nézet-Séguin had all the sound balances well in hand, and mezzo-soprano Leonard sang with a lack of affectation that was a joy to hear in contrast to Renee Fleming, who recorded the piece with a parade of her usual Fleming-isms. Here, the piece’s performance history had a clean slate that should help put listeners on the road to clearer understanding of the music in years to come.

‘Sheherazade,' with chemistry

Chemistry between Leonard and Nézet-Séguin truly kicked in with Ravel’s Sheherazade, a vocal triptych whose exotic texts — at turns fantastical, soulful and toxic — received incredibly specific orchestral support with the always-charismatic Leonard performing the three songs as a series of fully-developed characters.

Has she ever been this “on”? Most touching of all was the final song, “L’Indifferent,” about off-handed romantic rejection from a passerby, conveyed by Leonard with a combination of gravity, disappointment, and dignity that made you wish you were the one handing her the bouquet of flowers after the piece was finished.

Nézet-Séguin’s trademark with Ravel has been finding the underlying tension and continuity in the music, though Monday’s Daphnis et Chloe was unusually languid by his standards. Even the great flute solo had relaxed sensuality rather than inner passion.

The sheer sound of the orchestra was extraordinary, reminding you that after a season of pushing sound out of the Met orchestra pit, these players were ready to fill every cubic inch of Carnegie Hall. The audience erupted so loudly at the conclusion, you’d think they were Philadelphians.

A hypnotic ‘La Mer’

Debussy’s La Mer was less polished — inner voices could be muddy — though the interpretation was the most fascinating of the evening. Slow-ish tempos were used with such a hypnotic effect that the conclusion of each movement seemed to sneak up on you, and then deliver a second surprise in the final seconds with a usually-buried detail that put everything in fresh perspective.

As much as Ravel and Debussy are often mentioned in the same breath, Nézet-Séguin showed how much they inhabited hugely different worlds, with Debussy’s vision of the natural world and Ravel retreating inward into a mythological land of his own conjuring.

The Met orchestra returns with Nézet-Séguin on June 14, with the ensemble making a rare foray into Bruckner. The Philadelphia Orchestra program Friday will feature Stravinsky’s Funeral Song, Rachmaninoff’s Symphony No. 1, and Prokofiev’s Piano Concerto No. 3 featuring Beatrice Rana.

Information for the Friday and June 14 concerts: 212-247-7800 or Tickets: $22-165.