In orchestra years, a conductor in his 30s is a mere toddler, still framing out basic concepts of cause and effect as he moves through the world.

Yannick Nézet-Séguin is no toddler. He's 33, but already he has a sophisticated set of skills. The Montrealer, who made a Philadelphia Orchestra debut of considerable impact Thursday night, has the full concept of ensemble control under his belt.

With some gorgeous phrase-shaping and meticulously detailed dynamics, he put a personal imprint on Rachmaninoff's

Piano Concerto No. 2

. If he had to edge out the soloist a bit to make his point, well, at least the perspective was convincing - that this work can be heard as another Rachmaninoff symphony with regular visitations from the piano.

Add to all this an unpretentious, smiling, journeyman stage persona, and what comes across the footlights in Nézet-Séguin is an extremely promising talent.

Orchestraphiles will no doubt put down the fact that he had less to say in Tchaikovsky's

Symphony No. 6

as a function of this orchestra's extended tradition with the piece. But if you think about how many decades have passed since Eugene Ormandy and Riccardo Muti, and how few players remain in the orchestra from those eras, the factor at play here was a kind of rest cure for a composer badly distorted by Christoph Eschenbach.

One of the nice things about Nézet-Séguin - music director-designate of the Rotterdam Philharmonic - is that he doesn't make a spectacle of himself, even if he is a very physical presence. He made his mark mostly in an impressive climax here and there, and by taking a chance with a severe accelerando at the end of the third movement that paid off stunningly.

Wonderful. But in the rest of the work he had little original to say, and though it may have been beyond his control to bring the clarinets and oboe up to balance with the rest of the ensemble, one wishes he had at least tried. There's an operatic aspect to his phrasing, a singing quality that fits snugly with this ensemble's long-held value system. He had obvious buy-in on that one.

The Rachmaninoff, though - this was a real interpretation. The opening string sound wasn't especially cultivated by him, but the tempo was slow, the melody finely shaped, the mood unusually dour. Yes, he let the sound of the orchestra bigfoot over André Watts, which was a shame, since the pianist is ever the fascinating unstable element. Who was he on this night? He took fewer expressive chances than he often does, and his sound was more reserved than ever. A few flamboyant gestures stood to remind the listener what's possible in his playing.

It might have been his intention. Or maybe on this night, in the presence of a bigger personality, he was simply exercising a musical noncompetition clause.

Contact music critic Peter Dobrin at 215-854-5611 or pdobrin@phillynews.com. Read his blog at http://go.philly.

com/artswatch.
Additional performance: tonight at 8 in Verizon Hall, Broad and Spruce Streets. Very few tickets remain, $10 (last-minute rush) and $125. Information: 215-893-1999 or www.philorch.org.