We’ll never know what insights Rudolf Buchbinder and Ingrid Fliter might have brought to Beethoven in the opening two concerts of the Philadelphia Chamber Music Society’s piano sonata cycle. Both pianists pulled out. It hardly seems possible, though, that their replacements could have been more different from one another.

Louis Lortie opened the multi-week sonata-thon Tuesday night, and as a little present for stepping in he had asked that a Bösendorfer be brought in to the Perelman Theater. Which had the bigger-bone sound, piano or pianist, was hard to tell. But it was all of a single philosophy that you either liked or didn’t, this beefy, freewheeling way with Beethoven.

When Welsh pianist Llyr Williams arrived Wednesday night, the Perelman had back on stage its usual Steinway, and Beethoven sounded so different from the night before it seemed another species of music altogether. Williams is an astute colorist — the encore, tellingly, was Ravel, a particularly haunting “Valley of the Bells” from Miroirs — and the fluidity of his Beethoven was crystalline and smooth. Specific tones were meticulously chosen to suit the emotional intent of a moment — a brass-bright chord, a sinewy ornament. Never was Beethoven so elegant.

Yes, the repertoire of the two pianists differed, but that wasn’t it. The patron saint of artist cancellations intervened to make the point that Beethoven is, if not a blank slate, a very large one.

Pianist Louis Lortie
Elias Photography
Pianist Louis Lortie

I’ve enjoyed Lortie immensely elsewhere; there’s a recording of him playing and conducting the Mendelssohn piano concertos that is full of insight. Here, in Beethoven, I was less taken. To these ears, the Bösendorfer was muddy. Lortie got a fat bass sound and started notes with lovely, non-percussive articulation in Beethoven’s Piano Sonata in C Major, Opus 2, No. 3. The “Pathétique” was touching within moderate expressive boundaries.

In the Opus 57Appassionata” sonata, though, Lortie used a lot of pedal, and the piece became a sea of booms and echoes.

It was a relief to have the Steinway back Wednesday. For one, the instrument suits Williams. It suited the repertoire, too. The pianist took on five sonatas, including the Sonata in D Minor, Op. 31, No. 2, “Tempest.” The playing was streaked with imagination, and even in places that perplexed, Williams made you think. What was that erratic tempo all about in the first movement of the Piano Sonata in D Major, Opus 10, No. 3? It had the sensation of his chasing a soccer ball that kept getting away from him.

He took the second movement slowly, but that gave the drama room to grow into its terrifying buildup. There’s something un-pianistic in the last few spare notes of this music, a truly awful dip into bleak solitude. Williams made the movement a world unto itself, a desperation from which you were relieved to escape with the sunny first few notes of the next movement.

Jonathan Biss continues PCMS’s Beethoven piano sonata cycle Tuesday at 7:30 p.m. at the Perelman Theater, Broad and Spruce Streets. 215-569-8080, pcmsconcerts.org.