In the classical-music world, PLA means, not People’s Liberation Army, but Pierre-Laurent Aimard — the French pianist and, of late, conductor. They all get the itch to conduct, don’t they? As Jimmy Durante used to say, “Everybody wants to get into the act.”

On Friday night at Carnegie Hall, Mr. Aimard appeared with the Mahler Chamber Orchestra, “play-conducting.” That’s when you play and conduct at the same time. The Mahler Chamber Orchestra is one of Maestro Claudio Abbado’s creations. It forms the core of the Lucerne Festival Orchestra, which spent several days in our city.

Mr. Aimard began Friday night’s program with Mozart’s Concerto No. 13 in C major, K. 415. This is very seldom played, and it’s hard to say why: It is a fantastic piece (being a Mozart piano concerto, after all). The orchestra sounded superb: light and robust, graceful and full — and always warm, without a hint of scratchiness. The orchestra was in balance, in tune, in sync. And, best of all, very Mozarean.

Allow me to gripe for a second about play-conducting. It almost always harms your playing, your conducting, or both. Mr. Aimard was juggling a lot of tasks. He was conducting the orchestra, reading his music, turning his pages, playing the piano. You wind up conducting with your head, shoulders, and other body parts. And, worse, you conduct with your playing. That is, you alter your playing — its emphases and so on — in order better to lead the orchestra.

I’ll be glad when the play-conduct craze is over, if it’s ever over. Take the great Mozart pianists of the past: Haskil, Klien, Gieseking, Kraus, Lipatti, Casadesus, Rubinstein (yes), Richter (yes). They didn’t think it beneath them to collaborate with conductors.

That said, Mr. Aimard played pretty well. In the first movement, his playing was smooth and rounded — practically Chopinesque, at times. He was unexpectedly liberal with the sustaining pedal, making some of his playing slightly muddy — or rather, just a little blurred.

The middle movement, Andante, was less successful than the first. It was somewhat anemic, and excessively slow. The music seemed more Adagio than Andante — and it threatened to be shapeless. But Mr. Aimard did some inarguably lovely playing — inarguably lovely, slightly muddy playing.

In the closing Rondeau, Mr. Aimard was again smooth and rounded — and relaxed and polite. He might have been aided by more sparkle and vitality. This was laid-back, mellow Mozart, and hardly the worst thing in the world.

Next, a large team of union members removed the piano and reshuffled some chairs, and Mr. Aimard conducted a Haydn symphony: No. 102 in B-flat major. Mr. Aimard looked the very model of the modern conductor — particularly of the modern “period” conductor: solid-black Mao suit; no podium; no baton. And he conducted capably. In his gestures, Mr. Aimard is both elegant and energetic — interesting to look at.

The orchestra played with outstanding unity, particularly for a group so large: You have heard chamber ensembles, such as quintets, sextets, and septets, play with less unity. Haydn’s first movement was sharply etched, but not blunt. Mr. Aimard proved a good observer of rests. Did Haydn’s humor come through? Not so much, but that was okay. And the principal flute, Chiara Tonelli, played brightly — brightly in both senses.

In the Adagio, we heard one of the Mahler Chamber Orchestra’s best qualities: Its sound was streamlined but not thin. The next movement, Menuet, was elegant, but had the proper touch of earthiness. It was clear in its rhythm, the music having a snap. At the same time, the rhythm wasn’t overemphasized — an increasingly common sin in minuets.

No. 102 ends with one of Haydn’s gloriously impish creations — he had a million of them. And the MCO scampered along delightfully. PLA is a fine conductor — not a poser or an imposer.

The second half of the program was given over to another piece in B flat — Beethoven’s Piano Concerto No. 2, Op. 19. Particularly in the opening movement, Mr. Aimard would have been advised to play out more. A certain shyness was not in his favor. And, in the first movement’s cadenza, he did not display his usual command. That is, he didn’t have his usual technical control.

In the Adagio, Mr. Aimard and his forces were slow, stately, and warm — also a little plodding. At least at first. Eventually, however, the music breathed beautifully.

And the Rondo, that playful, joyful, eternally lovable thing? It was okay — a little dull. As before, Mr. Aimard could have used additional sparkle and vitality.

But the audience cheered and cheered, and cheered and cheered. After several curtain calls — performers usually play an encore at the merest suggestion – Mr. Aimard made an announcement. He said there was “only one possible encore” to play on this evening: the rondo that Beethoven first wrote as the finale to his B-flat concerto. Mr. Aimard said, “Let’s compare.” The earlier rondo is not bad, being Beethoven — but the composer ultimately made the right choice.