Size was not what it seemed at the National Symphony Orchestra’s concert Thursday night. The first symphony — Haydn’s “La Poule” — was petite. The concerto — Brahms’s Second, for piano — was symphonic. Such unexpected contrasts were further woven into the music by the conductor, Andreas Delfs, who liked to make things very, very soft and then very, very loud, right from the start. The very opening of the Haydn, the first piece on the program, involved stormy outbursts interspersed with silences that were as precise and sharp-edged as if they’d been drawn by an architect’s pen.

Storm, indeed, was a leitmotif of the evening, as all three works presented a cloudy, darkened front. But the two symphonies on the program — the Haydn was followed by Kurt Weill’s Symphony No. 2, from 1933 — offered a mellifluous take on storminess, like a frowning child who keeps losing sight of his own dark mood.

Delfs whipped up the opening of the Haydn into a romantic frenzy. The work’s classicism came through in how the piece kept dwindling down to combinations of one or two voices — something the conductor emphasized with dramatic pauses, or by keeping the music playing at a mere flicker, damped down to almost nothing.

The Weill work’s pose of seriousness came partly from within. Weill was one of many composers throughout the 20th century whose facility in more popular forms (read: musicals) led him to feel that he had something to prove in ostensibly more ambitious ones. This symphony feels as if it’s striving to put a high-art stamp on a natural tendency to break into song.

It’s sad that some people still feel it needs justifying; this symphony shows the same kinds of abruptly shifting moods and contrast between highbrow and lowbrow that have become staple fare in the concert hall in the symphonies of Gustav Mahler. But one sensed that the composer was making an effort to tamp down exuberance — stifling, for instance, little jazzy licks at the end of the second movement with frowning, somber tones from the rest of the orchestra. Delfs’s tendency to be a little ponderous probably didn’t help.

The program as a whole might well have been conceived as a pendant to an NSO concert in 2009 that also offered two shorter works alongside a Brahms concerto, and which was to have been the NSO debut of the pianist Nelson Freire. Travel restrictions spurred by swine flu, however, kept the 67-year-old Freire from leaving his native Brazil, so his debut with the orchestra was not then, in Brahms’s First Concerto, but in the Brahms Second Concerto on Thursday night.

The concerto, of course, represented the meat of the program, a 50-minute, four-movement behemoth and repertory staple. But it, too, presented unexpected contrasts. First, there was Freire, whose name usually comes attached to the epithet “reclusive” and who plays with a kind of sensitivity and lightness and nuance that doesn’t fit the stereotype of the thundering virtuoso. Add the NSO’s lean, even thin tone and Delfs’s finicky precision, and you sometimes got understatement, sometimes dullness and sometimes something quite buoyant and wonderful — like the moment when the beautiful, extended final chord of the third movement gave way to the playful, springy opening of the fourth movement, creating a marvelous sense of continuity. And Delfs’s thinning out of the sound bore fruit in solo passages, particularly the distinctive cello solo that opens the third movement.

In the second movement, dark and passionate, it became clear: Here, at last, was the storm that the music had been working up toward all night.

The program repeats Friday and Saturday nights at 8.