More than one conductor will tell you that while the music of Mozart may look simple on the page, the myriad challenges that music poses are anything but simple. The composer, after all, wrote for a very different kind of orchestra, concert setting and audience than exist today. The very perfection of his creations belies the bewildering number of choices available to modern interpreters.

So the question arises: How can music so indelibly wedded to the aesthetics and performance practice of late 18th century classicism be brought alive, in all its infinite expressive variety, for early 21st century ears?

Manfred Honeck, the Austrian-born music director of the Pittsburgh Symphony, hails from the same country as Mozart and no doubt has grappled long and hard with the problem. The all-Mozart concert he conducted with a chamber-orchestra reduction of the Chicago Symphony Orchestra Thursday night at Symphony Center posited several solutions. Energy and grace wrestled for supremacy. In the end, energy won out.

Careful planning evidently went into the program, which surrounded two familiar masterpieces — a piano concerto and a symphony — with contrasting vocal works that turn up less often in concert. British pianist Paul Lewis assumed the solo duties for Mozart’s Piano Concerto No. 27 in B flat (K.595), and Swiss soprano Regula Muhlemann sang a motet and two arias. Both soloists supplied the element that seemed to be in short supply elsewhere in the concert: charm.

Lewis’ finely poised account of Mozart’s final piano concerto reminded one that it was with Mozart’s music that he had made both his Chicago recital debut in 2008 and his CSO debut the following year.

His affinity for the Viennese classical style echoes that of his teacher, the great Alfred Brendel. Lewis is his own man, however, when it comes to the pellucid fluency of his runs, the crispness of his articulations and the suppleness of his phrasing. Above all, he brought a gracious, singing quality to the long Mozart line that always flowed naturally out of the music and kept the horizon firmly in its sights. The orchestra’s alert accompaniment was at one with the pianist’s purposes, as was Stefan Ragnar Hoskuldsson’s dulcet flute obbligato in the opening movement.

The arias Mozart wrote for individual singers get scant attention at symphony concerts, so Honeck’s inclusion of two of them — the “Laudamus te” from Mozart’s Mass in C minor, and “Vorrei spiegarvi, oh Dio” (K.418) — was welcome, particularly in Muhlemann’s gleaming performances.

The young soprano, who was making her CSO debut, introduced herself with a zesty “Exsultate, jubilate” (K.165) before getting down to more demanding coloratura business with the two florid arias Mozart wrote for women in his life — one for his wife Constanze, the other for his sister-in-law Aloysia Weber.

Their two-octave-plus range tested Muhlemann’s technique to the max, and she negotiated them with bright, pure tone and all the agility and precision these showpieces require. (It was pure cruelty on Mozart’s part to expect a singer to leap from a low B to a high E in “Vorrei spiegarvi.”) If her sound was weak at the low end of her range, what a pleasure it was to discover a Mozart singer of such style, who clearly is going places in this repertory.

Honeck’s accounts of the “Clemenza di Tito” Overture at the beginning of the program and the Symphony No. 35 in D (“Haffner”) at the end were, overall, a long way from the sunny Mediterranean Mozart Chicago audiences are accustomed to hearing from Riccardo Muti.

Fast sections were taut and energized to a fault, as if Honeck were channeling the aggressive manner Georg Solti would bring to this repertory. The Austrian’s hyperactive podium manner, with its emphasis on whiplash attacks and clipped rhythms, also brought Solti’s Mozart to mind.

The “Haffner” symphony began with an Allegro con spirito Honeck drove at a fairly unrelenting clip. Fortunately he relaxed his grip enough in the middle movements to allow the music’s courtly elegance to have its way. There was nary a hair out of the place in the performance. Was Honeck trying to apply period-ensemble aesthetics to modern-orchestra Mozart? If so, the synthesis of impulse felt incomplete.