You get to be young for a long time in the classical music world. Joerg Widmann has been a wunderkind in Germany for years — as a clarinetist who regularly plays with the world’s leading musicians and as a much-feted composer. Although he’s been on the scene for a couple of decades, he’s still younger than 40, and it was with his wonted boyish mien — albeit belied by a sprink­ling of gray hair — that he took the stage of the Kennedy Center Concert Hall on Thursday night to introduce himself to the National Symphony Orchestra audience in both musical capacities simultaneously.

He was preceded by his piece “Armonica,” a 16-minute feast of what appeared to be sound effects, built on the ubiquitous idea of a musical work growing from nothing into a cascade of sound and dying away again. The idea here had a visual echo in the solo glass harmonica at center stage. In appearance, it was an elongated cone of glass; in the hands of the soloist Christa Schoenfeldinger, though, it produced eerily artless melodies — like a song sung by a long-dead child — that were supported by the bevy of percussion, wind sounds and even a solo accordion player around it.

“Armonica” was Widmann’s contribution to the Mozart year, citing an instrument for which Mozart wrote but using it here in an eminently un-Mozartean manner. There was nothing classical about the piece apart from the sound of the instrument rising out of it like a recorded sound from an era before recording.

Widmann’s physical entrance filled the negative space that his piece had created by bringing both composers — himself and Mozart — front and center. In Mozart’s clarinet concerto, he showed himself as an elegant, slightly cerebral soloist who plays a mean clarinet, with subtle phrasing, crack fingerwork and a certain amount of moxie. Conductor Christoph Eschenbach and the orchestra offered robust accompaniment that was, if not exactly classical either, at least hearty.

The audience received Widmann with deserved raptures. It’s not every day that you encounter a musician who is equally good at two different forms at the same time. Widmann also happens to be breaking into conducting — he’s recently become principal guest conductor of the Irish Chamber Orchestra — but on this occasion, he left the podium to Eschenbach.

Composer and clarinettist Joerg Widmann has been a wunderkind in Germany for years — as a clarinetist who regularly plays with the world’s leading musicians and as a much-feted composer. (Felix Broede/Courtesy of Harrison/Parrott)

The evening showed Eschenbach in many ways at his best as well: as a promoter of young talent and as a conductor for whom nothing is ever routine. His style might not be to everyone’s taste, but there’s no arguing with the fact that the music matters to him — and there is something very compelling about the intensity he brings to it.

The second half of the program offered a counterweight to late Mozart in late Schubert: the “Great” symphony in C Major. Eschenbach paid attention, in some form, to every detail, plunging deeply into a work he conducted without a score. The NSO might not have always played with a rich sound, and it might not have always offered the kind of cohesion that would truly make these melodies melt. And a moment like the final chord of the second movement exemplified a drawback of Eschenbach’s style: It was beautifully shaped but not particularly balanced. Yet the performance had a scrappy determination that, in some ways, had more to offer than a more polished effort.

The evening provided beloved repertory with a touch of something new, seasoned with the genuine significance of the performance. It represented just the kind of the thing classical audiences like and showed why they have reason to like it.