ISO music director Mario Venzago triumphed with one of Beethoven’s greatest instrumental jewels.

With a lyric essence overriding a plethora of emotions and supported — but not dominated — by a pianistic display characteristic of Beethoven’s maturity, the Fourth had all its stops pulled by the Venzago/Ohlsson/ISO team. From the solo piano’s opening chords to the work’s energetically genial conclusion, they exuded a warm glow. Venzago had found the perfect work to coalesce his often-discussed rapid “Classical” tempos with his “espressivo” style. Venzago’s pauses electrified as intensely as Ohlsson’s passagework. Nowhere was this synergy more profoundly moving than in the magical transition from the Andante con moto to the brilliant Finale.

Whatever Ohlsson’s approach to the Fourth has been with other conductors, his concept fit Venzago’s like a hand in a glove. Following a standing ovation, Venzago encouraged Ohlsson to play an encore, and the pianist responded with Chopin’s Waltz No. 5 in A-flat, Op. 42 — a perfect follow-on piece to the Beethoven. Instead of stopping there as he should have, Ohlsson then offered a brief Scriabin display étude, actually detracting a bit from the preceding.

Venzago began this all-Beethoven program with a well but seldom performed Leonore Overture No. 1, Op. 138, actually the third of three overtures named for the composer’s original title to his only opera, Fidelio. The numbering of these overtures has often been described as a historical quirk: No. 2 — a long, distended, dramatic piece — was the first, coming in 1805 for the opera’s premiere. Beethoven then realized that he could make it more effective by condensing the material and tightening the structure, and produced No. 3 in 1806. This one has remained the most tautly dramatic, most popular and most effective one for concert performance. The presently played No. 1, a much slighter work, is now thought to have been written for a Prague production in 1807 that never took place. When Beethoven changed the opera’s title to Fidelio, he wrote a yet-lighter-veined fourth introduction, now simply called the Fidelio Overture, first used in 1814.

Are you as confused as I am? Also presenting a melding of nimble Allegros with expressive ritards, Venzago finished with a mostly effective Symphony No. 7 in A, Op. 92. The conductor’s varied approach, including a convincing, seamlessly-phrased Allegretto movement, suffered slightly from a few imprecise moments in the well-articulated fast sections of the other three movements. More time with his players — which will happen next season as Venzago takes residence here — hopefully should resolve the difficulty.