A regular guest conductor here, Ton Koopman has brought the merits of Baroque invention to the ears of several generations of music listeners, and Bach’s Brandenburg Concerto no. 3 in G major was the familiar work with which the programme began. Commissioned by the Margrave of Brandenburg in an era when music patronage still largely governed composer’s careers, the six eponymous concertos were completed in 1721, and sent on to their patron as “Six Concertos for Several Instruments.” That modest inscription would hardly foreshadow their emergence as some of the most loved compositions of the whole Baroque period.

Scored for three violins, three violas, three cellos, and basso continuo, the Third Brandenburg is often supplemented by harpsichord, and Koopman served as both fellow musician and conductor here. He has developed a strategy of shorthand for leading with his shoulders and various positions of the head, and he uses his mouth almost as a third hand to open and close the others’ sound. The musicians were quick to pick up the independent solo voices, alternating their turns in the limelight. Indeed, throughout the Third, the clarity of the line (read: the sing-able melody) is paramount. That was compromised to a degree in the first movement; the line was not always as crisp as I’ve heard, but overall, the vibrancy of their playing, combined with the grounded, sage role played by the cellos and continuo, made what felt almost like an animated dialogue among arguing schoolchildren, and a glorious undercurrent of fresh texture came through.

One reason the Third appeals so much is that it makes a strong case for the dignity of the viola: those who see the instrument as the eligible − but widely overlooked − older sister of the violin can be pleased that it enjoys equal ranking here. The viola even occasionally and brashly crosses above the violin line, and that the violists smiled among themselves did not go unnoticed.

For his part, Koopman sat at the harpsichord facing the configuration of ten players rather than the audience, a posture that sequestered his conducting technique more than the usual convention. The “historically informed” performances Koopman has tirelessly advocated over the years, namely, dictated a harpsichord Adagio as a transition here between the two Brandenburg movements, rather than the usual two simple half-note chords. The insertion honours Bach’s own tradition of bringing his compositions into various other settings, but it was somewhat unsettling to see the other players standing idly in a semi-circle around Koopman, while he played furiously showing us only his back.

There was no question that the great draw of the evening was British cellist Steven Isserlis, who was slated to play Haydn’s Cello Concerto in D major, one of the most demanding in the instrument’s repertoire. It would be pretty hard not to like Steven Isserlis: a superb musician, soloist, chamber player, teacher, author and radio broadcaster, he seems to excel at almost everything he does. But on the Tonhalle stage, he endeared himself twice over by acknowledging his fellow players on the stage, and smiling at them and the conductor during his performance. True, Isserlis has a habit of staring out at a distant point in space somewhere off his right shoulder while he plays, presumably to find the power with which to perform his magic. Despite the fact that he hardly ever looks at his own fingers or the frets, even in the most complex of passages, his virtuosity and his phrasing are unparalleled. And when, at the end of a dynamic passage, he slowly makes an arc of the bow out into the air beside him, his other hand away from the cello in a gesture almost of supplication, his rapt audience almost gasped at the sheer beauty of the sound and the uplifting motion.

The very same morning of the concert, the cellist had tweeted “so lovely to see Haydn’s name written on the wall of Zurich’s Tonhalle as we rehearse his D-major concerto… like a benediction”. And a benediction this Haydn was. Even with one moment in the Adagio and the very last note of “Chonguri”, an entirely pizzicato piece by Sulkhan Tsintsadze, he played as an encore going somewhat awry, I would argue that there is no other living cellist quite as musical. With the power of his technique and command of his instrument, Isserlis takes us from the celestial to the underground, from the most poetic to the most savage expression. Yet, after the interval, he sat in an ordinary seat in the hall like the rest of us mortals to hear the rest of the evening’s performance. He was receptive to fans’ questions and comments before the Mozart began, and greeted others cordially on his way out. We all hope he’ll come back to Zurich soon.

Last in the programme came Mozart’s “Linz” Symphony, always startling for the fact that such density and glitter could be composed in just a mere four days. Koopman − his usual spritely, almost pixie-like presence at the podium − was again in his element. While his left hand’s gestures were no match for the sweeping exuberance of his right, he grinned, cautioned, almost pleaded with wiry determination. He pulled a Beethoven-like sound out of the work’s Adagio, called up delicate dance steps of silk-clad ladies in the Andante, capitalized on the three strong horns to set the dynamism and mood changes of the Minuet-Trio, and entertained a muscular push-pull of volumes and pauses in the final Presto. What began rather light-heartedly, moved into a dance mode that almost prefigures the great “Swing” sound of the 1930s. For Mozart, that couldn’t have been more unexpected or – for us in the audience – more welcome.