Leon Botstein and the American Symphony Orchestra opened their season at Miller Theatre on Sunday afternoon with what is arguably the greatest symphony ever composed.

Johannes Brahms’s Symphony No. 1 was the subject of Sunday’s “Classics Declassified” program, which included a talk by Mr. Botstein punctuated by musical examples from the orchestra, a full performance of the work in question, and a discussion period. Professor Botstein was really in a groove for this lesson, discussing such divergent topics as the perceived death of the symphony, the forbidding shadow of Beethoven, and the 20 years necessary for Brahms to complete his first foray in the genre. He had the audience in stitches as he plumbed the seedy depths of the sexual relationships between Brahms and both Robert and Clara Schumann. He countered head-on the misconception that Brahms was an atheist, stating that his religiosity was more personal than evangelical.

It was fascinating to follow a germ of an idea to its logical fruition. Brahms sent a postcard to Clara on which he wrote a tune that he had heard on vacation in the Alps. We experienced this melody played in its original form and recognized it as the prototype for the famous horn call of the finale. In turn, Mr. Botstein demonstrated what other gems were mined from the same musical vein.

Using Schoenberg’s essay “Brahms the Progressive” as a source, Mr. Botstein clearly demonstrated the subtleties of Brahms’s unique compositional style. He touted the C minor Symphony as a prime example of a composer writing on two levels, so both connoisseur and neophyte could appreciate its craftsmanship. This turned out to be an apt emblem for the talk itself. Everyone came away with a fresh, new knowledge of the piece.

The performance itself was splendid. Employing an ensemble exactly the same size as the original orchestra that performed the work in its premiere under Otto Desoff in 1876 — and thus much smaller than what modern audiences normally expect — the conductor opted for a swift Un poco sustenuto. This was Allegro designed to showcase the gritty athleticism of his forces.This raw-boned, accelerated style is now all the rage and I am grudgingly onboard with the approach. I would point out, however, that the movement is considerably less majestic at this speed.

Concertmistress Erica Kiesewetter deserves special praise, not just for her striking performance “singing” the tenor line in Bach’s Cantata BWV 162 during the explication section, but also for her fluid singing line in the Andante Sostenuto. Her exquisite portamento lead-in to her final extended solo note that closes the movement was simply spine-chilling. The string sound was a marvel of dynamic control — the little crescendos eloquent in their opulence — even as the ensemble sound as a whole was (by design) a bit thin.

The Un poco Allegretto e grazioso, what University College London professor Arnold Zuboff once called “the perfect movement of music,” was quite lovely and made the strongest case for the agility and dexterity of such a whittled-down ensemble. The clarinet playing, in particular, was comforting without succumbing to overstuffed Victorianism. Enough clean performances like this one, and I’ll reconsider my penchant for the conductors of the 1930s.

Especially impressive in the finale were the inner voices of the antiphonal strings, and the expressive timpani work of Jonathan Haas, which emphasized how much more power Brahms achieved with one drum than virtually any modern composer does with a few dozen percussion instruments. Mr. Haas also played the last passages correctly, finishing just a sixteenth note later than the full orchestra. It is surprising how many fail in this crucial effect.

The audience consisted of many of my own generation and even a few veterans of an earlier era. How many times have we individually heard the Brahms First? Hundreds? Thousands? Professor Botstein’s great gift to us all this day was the sense that we were hearing this masterpiece for the very first time.