Andris Nelsons conducts the pianist Jonathan Biss and the Boston Symphony Orchestra
in Mozart’s Piano Concerto No. 1. Photo: Hilary Scott

I find I’m always writing about how Mozart’s symphonic works get sold short in performance.He tends to get kid-glove treatment; the music is approached with such tip-toeing delicacy that a listener starts to wonder whether the performance is in fact a representation and not a parody of the Classical style.

That wasn’t the problem exactly with Piano Concerto No. 27, the Mozart selection that was played on Friday evening at Tanglewood. Ifanything, a little more stylistic awareness—crispness of articulation, brightness of tone, and the like—on the part of the Boston Symphony Orchestra would have been welcome. Rather, what seemed to be afflicting the BSO was a lack of concern. There was no sharpness of attack or conviction in the dynamics. The strings muddled their way through running passages that top-flight orchestral players should be able to sight-read. “We’ve got Mahler 9 on the second half, who cares about some dopey Mozart piano concerto on side A?”

Jonathan Biss did, for one. A consummate professional, he brought his accustomed care and sensitivity to the concerto, giving an intelligent reading all on his own. He had to fight for his tempo somewhat—every time he pushed for something a little more lively, Andris Nelsons (leading all of the weekend’s concerts) would pull it right back in the next tutti section. Taken in sum, the performance was agreeable enough, but that's the trouble with Mozart—it’s so easy to make this music pretty, yet so difficult to make it profound.

The orchestra that returned to perform Mahler’s titanic Ninth Symphony was almost unrecognizable. Here was pure grit, intensity, determination. Gorgeous Mahlerian sounds swelled from every section of the stage—big, warm, bristling strings, gnashing woodwinds, belching brass. Nelsons’s reading was perfectly paced, and showed a superb sense of the scope of the piece.

A feel for the folk inspirations of the interior movements is essential for capturing the character of this piece, and Nelsons rendered them perfectly, getting exactly the sort of tipsy playfulness needed. I think I can say with certainty that this was the best performance I’ve heard from Nelsons during his tenure as the BSO’s music director. His firm grasp of the piece never flagged, keeping sharp focus even through the endless coda of the last movement and slowly tapering out, dissipating faintly into the evening sky.

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Jean Sibelius wanted desperately to be a violinist. From the time he was a teenager he made a violin career his chief ambition in life, only to find that he had gotten too late a start.

Maybe it’s selfish, but in a way I’m glad he failed. Turning his efforts to composing, he left an extraordinary legacy in the symphonic literature. Unable to achieve a major performing career as a violinist, he instead gave us the most intensely passionate violin concerto of the Romantic era. On Saturday night Augustin Hadelich, the young German violinist, gave Sibelius’s concerto one of the most compelling performances that I've had the pleasure to hear.

In a conversation we had earlier this year, my colleague Jay Nordlinger described the Sibelius concerto as “pure ice.” It certainly can be, and many violinists have given excellent performances that arrest with their piercing clarity.

But this concerto can also be a riveting, hot-blooded experience, as Hadelich showed with his interpretation. Playing deep in the string, he approached the piece with more than a shade of roughness, making it more an emotional outburst than a steely-eyed declaration. Few interpreters have ever channeled the sorrow of this concerto’s slow movement so acutely. And in contrast to their indifferent collaboration on Friday, Nelsons and the BSO gave the accompaniment their all, matching Hadelich’s fury with fire of their own.

A habit of Hadelich’s (or rather a shtick, depending whom you ask) is to play a Paganini Caprice as an encore, even when it’s not quite de rigeur—after a Mozart concerto, say. Sibelius’s concerto can stand up to a flashy encore, no question, so one of the more famous caprices seemed in store: No. 1, or the “Hunt,” or even No. 24.

He shocked us all with an infinitely more mature choice: the Andante from Bach’s A-minor Sonata, in a realization that was calm, reflective, expressive, and beautifully voiced.

The symphony on Saturday’s program was that evergreen staple, Beethoven 7. This must surely be one of the most heroic pieces of music ever set to paper, a thrilling gallop, bounding triumphantly across open fields. Nelsons and company gave a fine reading, albeit a reserved one, too; while the first and third movements were plenty stirring, one might have asked for a little more energy in the finale. Reasonable minds can disagree, but I’ve always thought this symphony’s closing bars should feel as though they might fly out of control at any moment. Nelsons kept a firm hand on the rein.

This conductor has a particular talent, though, for balance. He likes to highlight supporting lines, forcing even an experienced listener to hear the composition of the music from a new angle. In this performance, it was the blaring brass in the third movement's majestic trio sections that especially caught my ear.

Saturday’s concert opened with a new-ish piece, John Corigliano’s 1986 Fantasia on an Ostinato. The ostinato in question, it turns out, is the famous one from the second movement of Beethoven 7, though it's not quoted verbatim until close to the end of the piece; rather, Corigliano separates the distinctive rhythm from its melody and explores the two separately. The imposing rhythmic motif, blared with abandon by the brass,recedes and is followed by a wailing, formless account of the melodic line in the strings. When the two are finally recombined, it seems almost an original stroke of genius. An hommage of such imagination, variety, and power is a rare treat.

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A problem common to student orchestras at all levels is turnover. No matter how talented the players in the ensemble, the constant shuffling in and out of personnel makes it just about impossible to achieve the kind of sonic unity that we’re used to hearing from the major professional orchestras. From your area youth orchestras to the symphonies of Curtis and Juilliard, all are afflicted to one degree or another.

The Tanglewood Music Center Orchestra is about as polished a “student” orchestra as you'll find. Most of its members have already finished their undergraduate training and are pursuing or have completed Master's degrees in music. Yet for them the problem of personnel change is especially acute; playing together for just a couple of months in the summer, and led in performance each week by a different visiting conductor, they have scant opportunity to jell into a real ensemble.

Their accompaniment of Paul Lewis on Sunday afternoon, playing Brahms's Piano Concerto No. 1, included some very fine playing, a few miscues of coordination notwithstanding. The tone the strings produced at times in the Adagio was sublime, floating a gauzy hush over Lewis’s whispering playing. But on the whole they sounded detached, especially in the outer movements, where real conviction is called for. Lewis, for his part, played as he always does—with cool intellect, making his argument with glowing tone and crystalline phrasing, even if he did not tap into the music’s passionate extremes.

An orchestra with as much talent on its roster as the TMCO has in any given year can, given the right direction, deliver a performance worthy of any professional ensemble. Their account of Brahms’s Symphony No. 1, under Nelsons’s guidance, was polished, but more importantly, it was grand, majestic, imposing, true to the core of the work.

Every facet seemed perfectly shaped: the compact energy of the opening movement, the warm sighs of the Andante, the noble swelling of the finale. Nelsons molded the players into one finely tuned instrument, drawing from them a stunning interpretation of a touchstone symphony—one that any of the Big Five orchestras could have been proud of.