The final seconds of the Sibelius

Symphony No. 5

, as this beautifully textured symphony funnels down to a series of oddly spaced unison chords, have inspired puzzlement, awe, and ongoing blog debate. How should they feel? What do they mean?

With that as background, the Philadelphia Orchestra gave a particularly splendid performance of the piece Thursday under music director Yannick Nézet-Séguin, full of long, sweeping lines, epic gestures, and deeply informed treatment of the piece's vividly descriptive effects. The huge flock of birds rising up over a bleak Finnish landscape in the first movement, the almost unbearable sense of leave-taking in the final movement, and much else in between, tapped the orchestra's famous sound in ways that went well beyond surface luster, but that sound gave stature to the music in ways that a lesser orchestra could not.

Since the poetic high points in most Sibelius symphonies happen in moments of the sparest of scoring, the performance was most notable for its hushed, soft playing, suggesting the composer was showing how nothingness has its own kind of abundance. (For more on that front, consult composer John Luther Adams, inventor of Alaska impressionism.) Nézet-Séguin's grasp of the music's form meant that however much these flourishes seemed to expand into the symphonic horizon, they were in their rightful places.

And then . . . the ending. Nézet-Séguin left extra space between those final chords, so much that the music's thread threatened to be lost, and felt expressively inhibited, especially as not all these isolated chords were as cleanly stated as they could have been. These things happen, particularly with a conductor who isn't falling back on received wisdom - also true in the Peer Gynt selections that opened the concert, in which even Grieg's smallest grace notes had an extra snap and sense of renewed purpose.

In contrast to his CinemaScopic Sibelius, Nézet-Séguin took an opposite approach with Bartok's Violin Concerto No. 2, finding pockets of dance, comedy, mystery, and dissonant grumpiness that no conductor I've heard has explored with such relish. The music strained a bit at the seams, though soloist Gil Shaham firmly sustained the piece's lyricism, helping to carry the ear through the particularly detailed thickets of the orchestration. Shaham didn't always project his lovely tone to my seat in Verizon Hall. But at the slightest hint of coordination issues, he charmingly moved in closer to Nézet-Séguin. Some concertos can seem like simultaneous monologues from soloist and conductor. These two truly collaborated.

The program will be repeated at 8 p.m. Saturday at the Kimmel Center. Information: 215-893-1999