Playing Mozart and Beethoven on modern orchestral instruments is a risky business these days. Without the cachet of period performance style, or an early music specialist as conductor, orchestras can seem conservative and out of touch in this most familiar repertoire.

Christoph von Dohnanyi's programme with the Philharmonia Orchestra paired Beethoven's First Symphony, in C major, with Mozart's Requiem. A conductor steeped in the traditions of romantic music and one of the world's most luxurious orchestras: nothing suggested a hint of interpretative innovation. But Dohnanyi's performances were startlingly invigorating and insightful. His musicality and the Philharmonia's dynamism proved there is still vigorous life in modern orchestral playing styles.

The fascination of hearing Beethoven's earliest symphony, composed in 1800, with Mozart's final, unfinished work, written only nine years earlier, is the great difference between their styles and sound-worlds. The symphony bursts with the revolutionary confidence of Beethoven's maturity, while the Requiem has sombre colours and baroque forms.

The First Symphony is the Cinderella of Beethoven's symphonic canon - often regarded as nothing more than an attractive, Haydnesque joke. But Dohnanyi treated the piece with the seriousness it deserves, making it both the apotheosis of classical style and a precursor to a wilder romanticism.

After the extraordinary, ambiguous opening (Beethoven begins the symphony in the wrong key, only finding C major just before the allegro), the first movement was a study in focus and energy. Dohnanyi's brisk tempos never allowed the second movement to flag, while the swift menuetto was full of violence and daring. The headlong finale capped this fine performance with fiery energy.

With the Philharmonia reduced to chamber forces, and the relatively small forces of London Voices, Mozart's Requiem was a curious mix of intimacy and grandiosity. Where his tempos were sometimes extreme, there was a fastidious attention to detail in the balance and phrasing. And while London Voices may have been small in scale, their sound was full of voluptuous vibrato and vivid drama.

The soloists were also operatic, with Reinhard Hagen's booming bass, Toby Spence's plangent tenor, the outstanding mezzo of Alice Coote and Christiane Oelze's soprano. Their voices matched beautifully in the Tuba mirum and Recordare, but it was Coote's evening: she created a heartrending immediacy in some of Mozart's most exquisite music.