Young, fresh, accomplished, and famous are four words that handily apply to the British cello/piano duo of Sheku and Isata Kanneh-Mason, whose sellout Philadelphia Chamber Music Society debut at the Kimmel Center’s Perelman Theater on Tuesday was evidence that their international recognition is a done deal.

Sheku, now 20, captivated the larger public playing “Ave Maria” at the 2018 royal wedding of Prince Harry and Meghan Markle, amid a sea of celebrities and wedding hats. His forthcoming recording of the Elgar Cello Concerto, conducted by none other than Simon Rattle, is a high-profile release next month. But that’s hardly the whole story. He hails from a large, hyper-musical family, in which his sister and recital partner Isata, 23, is easily his equal; she released a disc of Clara Schumann piano works earlier this year.

It’s the famous part that’s worrisome. The ease and naturalness of their communication in a program of Beethoven, Rachmaninoff, Barber, and Lutoslawski wasn’t the most profound music-making but was something to treasure, reminding you that classical repertoire need not be a rarefied expression but a natural part of everyday living.

For Sheku, the cello seems to be an extension of his arms, so much that he is able to look at the ceiling while playing, monitoring his fingerboard only in the tricky upper range. His light baritone tone quality often blossoms coloristically within the bounds of a single note. In fact, it’s hard to really talk about individual notes in his playing because so much of what he does comes off in lyrically rendered sound shapes. Isata seemed not to be the least bit challenged by Rachmaninoff’s formidable keyboard writing. But notes weren’t just there; she had arresting coloristic resources to go with them.

Such qualities don't always survive the glare of recognition.

Beethoven’s variations on the Mozart aria Ein Madchen oder Weibchen was like a ping-pong game, in the best sense. Lutoslawski’s Grave, which lives up to its name in a way that only 20th-century Polish music can, didn’t feel at all incongruous, with its series of haiku-like gestures played with as much identification as Mozart.

The equal partnership demanded by the Barber and Rachmaninoff cello sonatas reflected smart planning. The Rachmaninoff Sonata in G minor Op. 19 can seem like a frustrated symphony, so grand are its gestures and the emotions behind them. But the Kanneh-Masons seemed to say, “Down boy, you really are a sonata,” in a smaller-scale, emotionally direct performance with such a strong sense of overall continuity that they justified observing sometimes-ignored repeats. They made you glad that Rachmaninoff self-indulgently elongated the final movement.

Cello player Sheku Kanneh-Mason at a Philadelphia Chamber Music Society concert Tuesday night.
Matt Genders Photography
Cello player Sheku Kanneh-Mason at a Philadelphia Chamber Music Society concert Tuesday night.

The infrequently heard Barber Cello Sonata Op. 6 — written in 1932, when the composer was still a Curtis Institute student — is a curious work, full of volatile emotions that shift before they’re played out. Tragedy and exaltation morph into each other, back and forth, in a late-romantic manner that can seem like a throwback (not unlike Rachmaninoff) with momentary flights into something more modern. The choices made by performers along that emotional spectrum can radically change the complexion of the piece.

For the Kanneh-Masons, the sonata was as modern as anything written in 1932, with brisk tempos that emphasized how compressed the first movement is, rendering a more jagged musical silhouette — in contrast to the gentility that’s often expected from Barber. From this starting point, the sonata was more “of a piece.” The West Chester-born Barber may have seemed like a modernist turncoat in the 1940s with his fierce Medea ballet and other later works. But you heard that kind of music bubbling closer to the surface in this performance of the Cello Sonata. So the performance wasn’t just good. It was original.

.