If you’re going to give a violin recital in Carnegie Hall, you might as well start with arguably the greatest violin sonata ever composed: Beethoven’s Sonata No. 9 in A major, Op. 47, known as “the Kreutzer.” And that is what Sarah Chang, the young American star, did on Tuesday night.

But from the opening measures, it was clear that Ms. Chang was not in good form. Her sound was uncharacteristically weak and squawky and yuck. She sounded like a sick singer, whose throat could not get cleared. And her intonation was pitiful.

Moreover, she interpreted Beethoven’s first movement oddly, almost eccentrically. She went in for some rushings, and then some bizarre slowings. The music was out of shape.

But, as every pianist knows, Beethoven entitled these works “sonatas for piano and violin” — note the order. And Ms. Chang had with her an excellent pianist, the Briton Ashley Wass. He played with command, elegance, and a sure sense of the musical line. And he has learned the art of playing boldly without pounding.

It was he who started the second movement, and he did so beautifully. He phrased the theme with true refinement. The tempo was slowish, but justifiable. Later, Mr. Wass showed us some fluid turns and passagework. And the man seems incapable of playing a wrong accent, which is a huge blessing.

Ms. Chang, too, did some nice playing in this second movement — she made some sweet sounds in her upper register. But her sound in general continued to be poor, continued to be sickly. And her playing was just slightly laborious, which is a bad quality for this music (and most any).

The Finale — marked Presto — the performers started at an unusually slow tempo. That’s okay, but if you’re going to be slow, you should play with extra character. And, from Ms. Chang, we did not have this character. Furthermore, she sped up later, before slowing again. This was not so much freedom in interpretation as confusion.

Mr. Wass continued to impress, summoning what you might call an elegant majesty. But, in keeping with the overall spirit of this account, he indulged in some absurd pauses.

I must say that it was greatly surprising, if not shocking, to hear Ms. Chang play as poorly as she did. It would not be too much to say that she was amateurish. And that is not Sarah Chang.

She began the second half of her recital with a new work by Richard Danielpour, the American composer (b. 1956). This was “River of Light,” dedicated to the memory of Isaac Stern. Mr. Danielpour says that it is about dying, or crossing over, and that it is his “attempt to prepare for the inevitable.” This is a gentle, songful, flowing piece, touched with mystery. Its ending is not exactly an ending — you feel a sense of moving on.

I give this piece a high commendation: I’d like to hear it again.

Ms. Chang played “River of Light” well, not trying to do much to it, letting the music speak for itself. The pianist again showed his uncanny ability to play robustly and smoothly at the same time. And he again showed his understanding of line.

Afterward, the composer joined the performers to take a bow. He looks rather like the conductor Riccardo Muti.

To end the program was a wonderful work by Prokofiev, his Sonata No. 2 in D major. This began life as a flute-and-piano sonata, but violinists — David Oistrakh, in particular — coveted it so much, they persuaded Prokofiev to transcribe it for them.

Ms. Chang traversed the first movement adequately, if not with complete musicality. The second movement, the Scherzo, could have been a bit wackier, and a good deal cleaner. The violinist was still not herself. And the third movement, the Andante? This music is what writers like to call “deceptively simple,” and Ms. Chang played it decently, although she could have offered more lyricism and grace.

As for the last movement, it was rhapsodic and full-hearted and not unexciting. But it was still sloppy and not especially distinguished. And someone should tell Ms. Chang that it does her no good to pound her foot on the stage. She was wearing a long dress, and it took some of us a while to figure out where those alarming, distracting sounds were coming from.

The pianist, I should note, hardly put a foot wrong in the Prokofiev, just as he had hardly put a foot wrong in the previous pieces.

So, Sarah Chang had a bad night — a quite bad night. Even stars are entitled to such nights, although one doesn’t want them in Carnegie Hall. At any rate, Ms. Chang is a personable, gracious, and appealing woman. She smiles and nods at the audience when they applaud between movements. She is patient with flash cameras. Yes, she had a bad night, but she will have better ones, and possibly only better ones.