Beneath the watchful gaze of a Founding Fathers portrait, the Eclipse Chamber Orchestra delivered a sterling performance of Mozart works on Sunday afternoon at the George Washington Masonic Memorial in Alexandria.

Under the baton of conductor David Teie, the chamber group kicked off its final concert of the season with the overture to “Lucio Silla” K. 135, a piece so rarely programmed that not even the 19 musicians onstage — most of them National Symphony Orchestra members — had ever heard it performed live. And what a treat it was, a 10-minute montage of Mozartean elegance, wit and energy, played with reverential warmth.

The ECO featured two of its own, violinist Joel Fuller and violist Mahoko Eguchi, in the Sinfonia Concertante in E-flat, K. 364. The soloists were so synchronous in timing, timbre and technique throughout the three movements — especially in the Andante — that their expressive melodic lines coaxed the orchestra to support the music in kind with sensitivity and sentiment. Together, the musicians took delight in articulating the score as Mozart had intended.

If the Sinfonia Concertante was all about the strings, then the Serenade No. 9 in D Major, K. 320 (“Posthorn”), was all about the winds. Joined by two flutes and two trumpets to complement the horns, oboes and bassoons, the ECO produced a full orchestral sound that compressed and swelled responsively to Teie’s conducting. Flexing their phrasing skills, the flutes turned Mozart’s melodic material into balletic pirouettes, spinning lines fluidly to the oboes for their delicate treatments.

Jean is a freelance writer.