The Chamber Orchestra of Philadelphia doesn't end its season with a bang, but with the sort of alternative mandate in which Mozart's less-often-played

Symphony No. 29

is an appropriate grand finale.

Other conductors might have questioned that at Monday's concert in the Kimmel Center's Perelman Theater: The 18-year-old Mozart was turning out consistently pleasant music at that time, but not mature masterpieces. Still, music director Dirk Brossé told the audience that it rates high among his favorites, so one had to trust that he hears something others miss. And he does.

Though often regarded as hailing from an elegant, purposely lightweight musical era that Mozart was soon to transcend, the Symphony No. 29 was a piece that the aging legend Herbert von Karajan maintained in his late-in-life touring programs, and he gave it a weight that bordered on ponderous.

Brossé more deftly walked a line in a piece that looks backward and forward in equal measure, making sure the music kept its innate friendliness but often finding rhythmic vitality in the final movement, suggesting that the piece doesn't exist entirely to please.

More sparks flew with the Sinfonia Concertante K. 364 with violinist Elissa Lee Koljonen and violist Roberto Diaz as soloists, both locally based and with strong Curtis Institute associations (she's a graduate; he's the president). Mozart is so scrupulously fair to both solo instruments that the piece can take on a now-it's-your-turn formality. Brossé isn't one to let that happen, and Diaz played with such an aggressive pulse, even during accompanying figures, that he seemed to be spurring on the performance with a touch of impatience and faster tempos. It worked. By the third movement, the ensemble was playing with heart-in-mouth brinkmanship.

I'm not sure Koljonen and Diaz were the best match. As much as I enjoyed her bright tone and interpretive ebullience, Diaz was more willing to set aside his honeyed tone for something less outgoing in terms of expression, giving the piece more layers of meaning and more detailed utterances.

The biggest surprises were Mozart's Adagio and Fugue in C minor, K. 546, his tribute to J.S. Bach that feels like a precursor to Beethoven's severe Grosse Fuge. As is his custom, Brossé added a bonbon of his own, Burt Bacharach Meets Wolfgang Amadeus Mozart, that borrowed melodic nuggets from "What the World Needs Now" and used them in a way that Mozart might have. Fun! Novel! But I hope he didn't spend too much time on it.