If, in the classical realm, technical mastery long ago became the norm, and if, more recently, greatness is as easily accessed as a YouTube search, what do we hope to glean from the live concert experience? Why go at all?

A smart curatorial hand assembling the weekend's artists and repertoire at the Philadelphia Orchestra affirmed the value of surprise. Saturday night in Verizon Hall could not have looked more unassuming on paper: a long-established violinist in a warhorse. But Nadja Salerno-Sonnenberg made Mendelssohn's Violin Concerto in E Minor into such a complete personal statement it left the impression it might never happen again (Sunday's repeat performance, broadcast live on WRTI-FM, came close). Without being extreme or eccentric, the violinist essentially rewrote a good deal of the work's performance tradition. Her opening material was worrisome - tentative and technically not quite under her fingers. But she rebooted with the second theme that established a startlingly more introspective tempo than is customary, and she created a world within a world that seemed almost a portrayal of some specific event in the composer's emotional life. Magic.

How to transition back from such moments was the trick, and here she had the benefit of Gianandrea Noseda. When it seemed she could not possibly speed the arpeggios at the cadenza's end to meet the orchestra's requisite tempo at their reentry, he made the connection, in its drawn-out stepping up of tempo, an expressive opportunity. He also often granted her a hush to make space for her sound. When she arrived more than three decades ago, Salerno-Sonnenberg was sometimes thought of as a freewheeling id. It seems less likely her psyche has changed than ours. Competent violinists abound. Convincing individualists we should hold close.

Noseda opened with Respighi's Ancient Airs and Dances for the Lute, Suite No. 2, pleasant tunes and inventive orchestrations. In Holst's The Planets, extremes sometimes paid off, sometimes puzzled. "Mars, the Bringer of War" burned furiously - wonderful. Concertmaster David Kim was weak in his "Venus, the Bringer of Peace" solos. The march in "Saturn, the Bringer of Old Age" was too fast to make much sense. There was something poetic about not seeing the 25 women of the Philadelphia Singers Chorale in the final movement, "Neptune, the Mystic" as the group prepares to disband in May. They were stashed in the acoustic chamber above the conductor's circle, their aural ether both authoritative and refined, their impressive contribution passing without so much as a bow.