The first thing to say is that she showed – that she didn’t withdraw. Martha Argerich arrived onstage at Carnegie Hall about seven minutes after 8 on Wednesday night, for her duopiano recital with Nelson Freire. Ms. Argerich – described in the first sentence of her official bio as “a living legend” – is a legendary backer-out, and you never know whether she will appear, until she actually materializes. You also never know how she’ll play. For a living legend, she can play disgracefully.

An Argerich concert is always a happening – a bit of a zoo – and there was indeed a buzz in the air at Carnegie Hall. Seating spilled over onto the stage. Ms. Argerich doesn’t play by herself all that often anymore, preferring chamber music, concertos, and recitals with her old friend Mr. Freire, a Brazilian pianist. (Ms. Argerich was born in Argentina.) New York is in a two-piano moment, as Emanuel Ax and Yefim Bronfman gave a duo recital in Avery Fisher Hall two weeks ago. On May 1, Evgeny Kissin and James Levine will play a four-hand recital at Carnegie.

Ms. Argerich and Mr. Freire began with Brahms’s Variations on a Theme by Haydn (a work that Messrs. Ax and Bronfman have just recorded, incidentally). We knew we were in trouble when Ms. Argerich and Mr. Freire over interpreted the theme. This should be played fairly straight, as Brahms will go to town later. And the pianists were unable to go right into the first variation, because Mr. Freire had to wait for a page turn. This was unfortunate – spoiling the musical effect that Brahms has arranged.

And as that first variation continued, it was disjointed, and way over pedaled. Much of the work would be played this way: the two pianists out of sync, indifferent, and sloppy. Amateurism reared its head. Tempos were too elastic, robbing the piece of its shape. It needs a certain rigor to succeed. Now and then, the pianists provided some smart and sensitive playing, but one grasped at straws. Ms. Argerich committed some of her harshness and percussiveness – a number of accents were ridiculous.

During the Brahms, and before the next work began, Ms. Argerich fiddled irritably with her bench, seeming to blame it for whatever problems she was having. I took this as part of her usual act – singers aren’t the only divas. I, for one, wanted to say, “It ain’t the chair, honey.”

That second work on the program was Rachmaninoff’s Suite for Two Pianos No. 2, Op. 17, one of the jewels in the two-piano crown. In the first of the four movements – Introduction: Alla marcia – Ms. Argerich and Mr. Freire were much improved. With the former, there is often a little animal excitement, and so there was here. And the two pianists were meshing better. The second movement, the Waltz, was not so together, but it had some nimbleness and sweep. The following Romance was, in my view, overly retiring: a little mousy and limp (and shapeless). But in the closing Tarantella, we heard some of the famous Argerich technique, in the form of very fast repeated notes. I was reminded that the composer was perhaps the greatest piano technician ever.

The crowd screamed and screamed for the two pianists – well, actually for one – bringing them back for numerous bows. And this was only intermission. I couldn’t help thinking, “Why don’t they applaud enthusiastically for good concerts? Usually, they barely let them leave the stage” (before heading for the bars and bathrooms).

The second half of the recital opened with Lutoslawski’s Variations on a Theme by Paganini – you know which theme: that marvelous A-minor caprice. It was fun to hear Lutoslawski’s treatment, and the pianists executed it with style and accuracy. This was probably their best effort of the night.

Then the friends met at one piano, to play a four-hand work: Schubert’s Rondo in A major, D. 951. (Schubert is the king of four-hand music.) This was rather dear, as it should have been, though stricter tempos at the beginning might have been wise: The Rondo was nearly rubatoed to death. And Mr. Freire might have given us a better singing line; his sustained notes were poor – sounding, then immediately dying. But he ended the piece with a lovely trill and turn.

The printed program closed with “La Valse,” Ravel’s dazzling take on Vienna. (Messrs. Ax and Bronfman also played this work, at Avery Fisher.) There was some decent playing here, although there was some rushing, and some of Ms. Argerich’s over aggressiveness: She pounded and slapped at the keyboard as though the music were Prokofiev’s (and it might not have been appropriate for Prokofiev). And when the pianists got to the climax … there was no climax. Shapelessness was a persistent error throughout the night. But the crowd loved “La Valse,” as they had loved everything else.

The players gave them four encores, of both the two-piano and four-hand varieties. One was “The Dance of the Sugar Plum Fairy,” slow and idiosyncratic. Also affected. The Fairy dances so nicely when not imposed upon.

On April 12, Ms. Argerich will play – is scheduled to play – Beethoven’s C-major concerto with the Philadelphia Orchestra, also at Carnegie Hall. It may not prove Beethoven, exactly. But it will most likely be an adventure.