Sixteen years ago a gregarious, chubby guy who had just turned 20 showed up at the first University of Maryland International Piano Competition and, to even his amazement, carried away the third prize. Then followed his concert debut, here at the Phillips Collection. These days the guy still plays the piano. He is Emanuel Ax.

Now Ax is back at the university as a judge in the newly renamed William Kapell Competition, and he played a recital at the Tawes Theater last night.

The mature Ax is one of the master musicians of our time, a truly formidable figure.

Yet the word "formidable" in the usual sense is not the idea. Ax doesn't play like that. In fact, plenty of his colleagues can play chords and scales faster and louder than he. And, as he did last night, he will miss a few notes from time to time. But beyond a certain point, he does not seem to care. During a visit here once, Ax was asked why he doesn't play a particular virtuoso showpiece, and he replied with wry self-deprecation: "How can I? It's too hard."

But what Emanuel Ax is brilliant at is vastly harder, and more valuable. There is his extraordinary mastery of tonal color, his unerring feel for the shape of a phrase and for where it fits into the larger picture, and there is his bewitching grace. These are qualities of an artist with a wonderful ear for nuance and, above all, a first-rate musical intelligence. He lavished all this on everything he played last night.

The opening Haydn Sonata in C-major, HOB. XVI/50, was vintage Ax. Nobody has mastered this kind of music more delectably. The work is so cheerful and so playful that most pianists sell it short. They don't realize what great music it becomes with sound as pearly, with passage work as even, with voicing as unforced, as Ax brought to it. And there was his unexcelled sense of timing -- in calculating a ritard, or in judging those false pauses in midphrase that dot the last movement.

*An utterly different kind of work, the Chopin B-flat minor sonata, came at the end. Its urgent passions were intensely caught. The great opening movement had unflagging force without ever seeming overdriven. The gradual crescendos of the funeral march were superbly controlled. And the sad legato melodies were beautifully phrased and colored.

There was a Brahms group right after the Haydn -- the two rhapsodies and the three Op. 117 intermezzi. The performances were controversial; one listener remarked during intermission, "We certainly heard some slow Brahms." And that was correct. But we also heard some beautiful Brahms.

The rhapsodies, especially, were understated, with almost none of that ferocity that a player like Glenn Gould brought to them.

The truth is, however, that reflectiveness is as much a part of Brahms as his anger. And the rhapsodies work either way. Ax's way of doing it reflects that expressive duality in Brahms that Leonard Bernstein talked about in his recent PBS series.

The first encore was the Chopin C-major mazurka, elegantly played. The last was a lovely version of Liszt's Petrarch Sonnet No. 123.