For a conductor, a good way to assert yourself in front of an orchestra is to lead it in something the musicians have never played before.

Juraj Valcuha, a 36-year-old Slovakian, asserted himself with particular force with the National Symphony Orchestra on Thursday night: Both pieces in the first half of the program had never been played by the NSO. Even more strikingly, one piece was a Mozart piano concerto (the 13th, in C).

When Valcuha made his debut with this orchestra in 2010, he led, among other things, the Szymanowski violin concerto. Obviously Szymanowski is his thing. His opening piece in the current program (which repeats Friday and Saturday) is Szymanowski’s first big orchestral work, a Concert Overture from 1905 that strongly evokes the early tone poems of Richard Strauss. They are big and bursting with ideas, now heroic, now languid and drooping and decadent, layering up orchestral timbres and topping them off with the thread of a violin or viola solo.

Valcuha is a strong and authoritative conductor who leads cleanly and doesn’t succumb to bombast; he can make big sounds without it ever seeming as if he is going to lose control. He managed to evade melodrama even in the emphatic ending of the Szymanowski, keeping things energetic and brisk.

And when he switched gears for the Mozart, the orchestra still sounded resilient and energetic and big. This was Mozart on a modern orchestra, with a modern piano, played with an understanding of classical style rather than what we now think of as a pure classical sound.

Jonathan Biss, the piano soloist, also continued a theme from his most recent NSO appearance by playing another Mozart concerto (in 2009, it was K. 595). Biss, 32, has been settling into, or arguably staking out, a new level of prominence in the past couple of years. That fact was audible, and visible, in his playing: His faux-dramatic gestures seemed more pronounced and his sound slightly more full.

He plays with a gorgeous legato, an evenness that gives the throwaway notes equal weight to the structurally essential ones, so that his ornaments in the first movement, in particular, felt slightly thick and yet flowed away effortlessly, calling to mind the simile once used to describe the voice of the soprano Rosa Ponselle: ball bearings moving through oil.

Some of Biss’s ornaments seemed to suspend time briefly, as if stretching the line to create room to hang little parcels of milli­seconds, like balls on a tree. Yet there’s an obedience to Biss, as well. Doing all this, he’s very much the good boy, an “A” student performing everything the way he’s supposed to. Kudos to him, however, for picking an unflashy concerto, one that ends appealingly with a quiet descent before a full stop. Rather than a towering
climax, it is simply, and with finality, done. One appreciated the matter-of-factness.

Valcuha returned after the intermission with two big French pieces that were roughly contemporaneous with the Szymanow­ski: Ravel’s “Mother Goose” suite and Debussy’s “La Mer.” He restrained himself here, too, keeping things emotionally precise, such as the transition from the Chinoiserie of Ravel’s “Laideronnette, empress of the pagodas” to the swaying lyrical waltz of the “Conversations of Beauty and the Beast,” the next movement. His “Mer” was a huge sea, but one that posed no threat to those on shore.

It’s nice to hear the NSO asked to be more exact. And these days, the orchestra is sounding good and is well able to rise to the challenge.