There’s a glossy perfection to everything that Ricardo Morales does. If you didn’t know better, you might think this is simply the way it is with clarinetists.

It’s not. Morales was soloist Thursday night with the Philadelphia Orchestra in Verizon Hall in Weber’s Clarinet Concerto No. 2 in E Flat Major — the concert is repeated Friday and Saturday — and he made the transition from his normal perch as the ensemble’s principal clarinetist to the front of the stage with his basic personality intact.

He is above all a refined player, even if all of the jumps, trills, and runs of the work were practically begging to trip him up.

Weber was the great innovator of his day, asking instrumentalists for a tall order of technical firepower. This work, though, also straddles the expressive worlds of Mozart and opera. The second movement has what amounts to a recitative, but for clarinet.

Morales didn’t miss the allusion to vocal drama, of course: He played one passage so softly it was a death scene in miniature. The third movement, based in dance, was pure adrenaline, with great speed and distance covered by a clarinetist who never seemed to break a sweat.

Orchestra principal double bassist Harold Robinson joined him in an encore: a particularly smooth, swinging "Calypso Serenade" from Morton Gould's Benny's Gig.

This program was to have been led by Andrés Orozco-Estrada, but the conductor called in sick and the run of concerts was taken over by Joshua Weilerstein. The program changed only slightly, with Caroline Shaw’s Entr’acte swapped into the spot originally meant for Janacek’s Taras Bulba.

The Shaw, first written for string quartet, was played in its string-orchestra version, and it was a funny thing to see these renowned string players in one of the work’s techniques that asks them to draw their bows across the instrument with such light pressure the only sound heard is a kind of (nearly) pitchless, airy effect. But there is a lot more to the short piece.

Its basic idea is soulful repetition. A figure comes forth in intermittent pulses. It reaches for completion, but something keeps stopping it. Aspects of it get developed, refracted, distorted.

Other sections, like the pizzicato one, seem to be feeding us melodies with some of the notes missing, as though those notes were obscured by an unseen scrim of silence. Shaw in the piece sounds to be on the verge of new techniques and expressive modes — like Weber.

Also retained from the original program was Brahms’ Symphony No. 3, and the piece was revealing. Weilerstein — artistic director of the Orchestre de Chambre de Lausanne and an offshoot of the musical family that includes sister Alisa Weilerstein, the cellist — was making his Philadelphia Orchestra debut with these concerts. The peek was promising.

It wasn’t clear that Weilerstein, 31, had much to express in the first movement, which he led within a textbook range of ideas on tempos and phrasings. Something changed in the last two movements, though. In the expressive and well-worn third movement, he used a quicker tempo to blow a fresh breeze through what can sometimes be a treacly wallow.

Weilerstein seemed to recognize in this music some of the same complexities of Brahms’ piano pieces. His approach had a healthy effect on the ensemble.

The quicker tempo set up Jennifer Montone for success in her lovely horn solo, and bassoonist Daniel Matsukawa had great presence in spots of bringing out inner voices. Morales, by the way, didn’t take the night off after the concerto, but returned to his usual ensemble chair.

You might have felt there were aspects of Weilerstein’s performance that would have benefited from more attention — some balances in the last movement, for instance. But he has a good feel for the long line in music and an original imprint on phrasing. That’s quite a bit right there.

Additional performances: 2 p.m. Friday and 8 p.m. Saturday in Verizon Hall, Broad and Spruce Streets. Tickets: $10-$153. Information: 215-893-1999,,