When Piotr Anderszewski, the Polish pianist, is good, he is very, very good — and so he was in recital at Carnegie Hall on Saturday night. He played to his strengths, too: Beethoven and Szymanowski.

He began with late Beethoven, the Six Bagatelles, Op. 126. Sometimes, Mr. Anderszewski can be a severe, harsh, cold pianist, as, say, Alexis Weissenberg can be – or Maurizio Pollini, or even the fabulous Leif Ove Andsnes. But, in the first bagatelle, he was all poetry: delicate and beautiful. His passagework was silky smooth. His softest playing, unfortunately, was thin and wispy; it did not really sing or carry. This would be a problem for Mr. Anderszewski — a trait — all evening long.

The second bagatelle, a fiery piece in G minor, was, indeed, severe — but not inappropriately so. It was bracing and exciting, rendered with great evenness (of line). As he continued with the bagatelles, Mr. Anderszewski played with all the qualities he needed: boldness, tenderness, grace. His dynamics were apt, and his phrasing was wise. He used a judicious amount of pedal — not too much, not too little. He showed a shrewdness about rhythm ( just as Beethoven is shrewd about rhythm). And he conveyed that nobility, that majesty — even a quiet majesty — so typical of the composer.

This was exceedingly mature playing.

The playing that followed was, if anything, better. Mr. Anderszewski is a champion of Karol Szymanowski, his countryman, and has made an excellent disc of his music (Virgin Classics). At Carnegie Hall, he played the three “Métopes,” called “poems for piano,” written in 1915. (A metope is part of a Doric frieze.) These are peculiar, Impressionistic, and wondrous works — otherworldly — and they are none too easy, for the pianist.

Between the bagatelles and the “Métopes,” Mr. Anderszewski did not give latecomers time to file in — which was thoughtless, especially considering how quiet and ethereal the first piece is. Dozens were thundering to their seats as Mr. Anderszewski was playing. But what superb playing it was! Mr. Anderszewski was exquisite in the Szymanowski, coloring like a pro. These pieces were so interesting musically, you almost failed to notice the pianist’s incredible virtuosity.

The third metope, Nausicaa, had an intoxicating swing. In fact, all three pieces were intoxicating, and delicious.

After intermission, Mr. Anderszewski played one, colossal work — more late Beethoven, the Diabelli Variations, Op. 120. Beethoven wrote 33 variations on Diabelli’s little waltz — three more than Bach wrote on the Goldberg theme — and they are a monument of compositional inventiveness and genius. Mr. Anderszewski has made a name with this work: His 2000 recording (for Virgin) was widely hailed.

You have to tuck into Op. 120 with command, sharply etching that waltz theme — and that is exactly what Mr. Anderszewski did. He kept his command all through this nearly one-hour piece, too. A work like this — not that there are many — requires extraordinary judgment, and this pianist has it. You could make some criticisms, but they would be small (and perhaps small-minded). For example, there was that too wispy, uncarrying soft playing. And occasionally Mr. Anderszewski would play superficially, on top of the keys. Most seriously, some of the slow variations were too slow — almost static — cheating the work as a whole of some momentum.

But look: This was a feat of pianism and a feat of musicianship. It was a feat of concentration, too. During the last variation — transcendent — some kind of electronic device went off, beeping and beeping. It could not be silenced for what seemed like eons. But Mr. Anderszewski was unfazed, even if the audience stirred.

I was doubtful there would be an encore after this magnificent marathon, but Mr. Anderszewski obliged us with the Sarabande from Bach’s Partita No. 1 in B flat. It was beautifully shaped, with the repeat of each half pleasingly different from what had come before. And it was beautifully embroidered, beautifully ornamented — seldom will you hear ornamentation so fine in Bach.

More encores? Yes — Mr. Anderszewski played, repeated, the first three bagatelles of Op. 126. I’m not quite sure what his purpose was, in part because I didn’t hear the explanation he whispered from the stage. But I am sure that he played these pieces just as well as he did the first time — not better, not worse.

And about those Diabelli Variations: I heard Serkin play them, and I’m glad I did. And although nostalgists will bust a gut: I am similarly glad that I heard Piotr Anderszewski play them.