In an interview with Charlie Rose a couple of years ago, Sir Simon Rattle made the startling comment that conductors only become “competent” after they turn 60. If that’s the case, it’s really quite difficult to imagine just how “competent” young Canadian conductor Yannick Nézet-Séguin might be after more than another two decades on the podium, particularly with a band in front of him as supple and giving as the revitalized – and no longer bankrupt – Philadelphia Orchestra.

Ravel’s La valse came first. La valse is usually treated as an orchestral showpiece, as either explicit or implicit encore material, but not here. Whether you think of the piece as a searing indictment of fin de siècle Vienna, a purely structural disintegration of a musical form (à la Boulez), or simply a celebratory, romping waltz, Nézet-Séguin provided plenty of each to satisfy. But it was the technical quality of the playing he extracted from the Philadelphia strings that struck most, with their infinitely subtle variations of tone and colour, their effortless portamento (so swooning as at once to be mocking and admiring their Viennese counterparts), and their sparklingly chatty phrasing.

What’s more, Nézet-Séguin extracted more than enough lucidity from the whole orchestra that one could marvel anew at the quality of Ravel’s orchestration. Here is a conductor who knows how, physically, to extract exactly the sound his vision of pieces like this requires. That vision was impressive, too: the mists parted grumpily, as if a hangover from the previous night’s dancing needed to be lifted (hair of the waltzing dog?), yet the first gigantic crescendo was judged crashingly enough to insist on another night on the floor. The final destruction of the waltz thrilled and chilled in equal measure, a fitting climax to an outstanding rendition of a work that’s tricky to pull off.

Shostakovich’s ever-popular Fifth Symphony was just as good, although here one started to see where work is still in progress for Nézet-Séguin. This was certainly a young man’s Fifth, though that’s hardly a problem. After all, not every performance of Shostakovich needs to be full of Soviet angst, nor weighed-down with anti-totalitarian political load. Shostakovich completed this symphony when he was in his very early 30s, and though he had undoubtedly been through a great deal by then, there is a young man’s optimism inherent to the piece. That said, (slightly) less extreme tempo relationships might have been beneficial here, and tension sagged in the slow movement.

Intriguingly, this was Shostakovich conducted for the most part as if it were modernist Mahler, and not just in the scherzo (for which Mahler’s Fourth seems a likely inspiration). It worked magnificently. Phrases were exaggerated, personalized, and there was an attractive flexibility to everything in the long opening movement. The Scherzo bit hard, cellos digging in with gusto, the Trio swooping around as if it were one of Mahler’s Ländler movements. The third movement, as had La valse, showed Nézet-Séguin to be an already talented conductor of transitions, although this Largo needed a longer-breathed, less note-to-note approach really to hit home. The finale, though, could not have been more triumphant, starting surprisingly slowly but transitioning, gorgeously, with a brutal smack to extremely high speeds reminiscent of the opening movement’s central sections. Quicker sections were whipped up, always on the verge of accelerating madly but never quite managing it, while rhythms were punched out. Those overly hammy final pages - always a test of whether the triumphs of this symphony have been earned in performance - seemed, for once, to be deserved.

In the context of two very good orchestral performances, Szymanowski’s final work, his second violin concerto, seemed an outlier. It was undoubtedly helped by the rhythmic pizzazz of the preceding Ravel, and there was much to enjoy, whether in Leonidas Kavakos’ assured playing and his seamless merging of folk tunes with other material, or the exquisite balances found by Nézet-Séguin. But the Ravel also pointed up Szymanowski’s murkier orchestration and sound world, and this performance never quite got off the ground. Still, the Ravel and Shostakovich were enough, far more than enough to carry a thrilling concert, and to show off a conductor who, one day much sooner than his 60th birthday, is going to be so much more than “competent”.