Violinist Pekka Kuusisto. (Kaapo Kamu)

The most delightful moment of Thursday night’s National Symphony Orchestra concert almost didn’t happen.

Violin soloist Pekka Kuusisto had taken three curtain calls after a lengthy and difficult (for both performers and listeners) concerto by Magnus Lindberg. Intermission was beckoning, and the applause subsided quickly. But Kuusisto bounded back onto the Kennedy Center’s Concert Hall stage just before it stopped, indicating that he wanted to offer an encore.

It was good thing he announced it, because the piece was strongly dis­orienting — simultaneously new and old, and seeming to come from everywhere: Appalachia, Arabia and Andalusia. But it was actually from a collection of 17th-century Finnish folk tunes, gathered by Samuel Rinda-Nickola. It scrambled the brain (in a good way) with its disparate strands. Conductor Christoph Eschenbach himself even came out to listen.

Our brains were scrambled in a different way by the two newer works on the all-Finnish program, which is the NSO’s contribution to the Kennedy Center’s “Nordic Cool” festival. Two Sibelius pieces bookended the Lindberg concerto and Kaija Saariaho’s “Orion” (both local premieres) — surely the largest quantum of unfamiliar notes that the NSO players have faced this season, and most of them eminently forgettable.

The Lindberg, at least, offered what could be called “themes,” dissonant and meandering though they were. Kuusisto, dressed in some dark Euro­trash assemblage, is a dramatic, loose-limbed and natural violinist who plays (and interacts) somewhat like a jazz musician: sometimes fiddling with his back to the audience, sometimes communing intently with one section or another — and generally having a bouncing good time.

It was difficult to assess the actual quality of his playing, first because the piece was gnarly and unconventional, and second, because Eschenbach let the orchestra run wild over him. Vast swaths of passage-work were inaudible.

Saariaho’s piece — essentially a three-movement symphony — was a true slog, almost devoid of actual musical interest. The first movement was a continuous, dense, caliginous mosaic of sounds with no discernible melodic elements. The second featured a succession of meandering solos by various instruments, calling to mind Mark Twain’s description of the Book of Mormon: “chloroform in print.” The finale called for much athletic bustling from the strings — a good bit of it faked — that was buried by the winds and percussion.

So much ado about so little. Eschenbach barely got one curtain call out of it.

What hurt the two premieres was their kinship with the great master of Finnish music. It is one thing to pair Mozart with, say, John Adams; the jarring contrast is itself the point, because no one is actually comparing the two. But here, to follow “Orion” with Sibelius’s glorious final symphony (No. 7) made the connections and the Himalayan superiority of the latter almost painful to contemplate. Here, finally was real music, where every note counted, and the NSO musicians sat up and played with care and involvement.

It was a fine performance, too. Other than some shaky transitions in the scherzo sections, the ensemble was very good. The players are starting to arrive at a mutual understanding, or accommodation, of Eschenbach’s often unclear gestures.

Balance issues aside, the brass sounded splendid. The NSO’s horn section, now predominantly female, is the glory of the orchestra. The opening work, Sibelius’s “Night Ride and Sunrise,” is one of his more obscure tone-poems, probably because the first section badly needs tightening, but again, the brass perorations in the final section were a highlight.

The program is to be repeated Friday and Saturday at 8 p.m. at the Kennedy Center.

Battey is a freelance writer.