The final works of two composers, left unfinished at their deaths, were vividly brought to life under the baton of Thomas Zehetmair at The Sage Gateshead. Bartok’s Viola Concerto, was left as a cluttered pile of sketches and fleshed out posthumously by his faithful supporter Tibor Serly. Any debate as to how much of the resulting score was actually Bartok’s was firmly laid to rest by Ruth Killius, who conveyed the spirit of his music in a compelling performance. The opening movement, with its stimulating mix of developing themes, was keenly articulated; the Northern Sinfonia providing fine-tuned accompaniment. Killius showed up the strengths of the viola as few could, negotiating the upper register with finesse and generating warm earthy tones at the lower end. The long singing lines in the slow movement were beautifully sustained, while the sudden bursts of energy and swirling folk music of the finale were delivered with unerring virtuosity. The Sinfonia Chorus sang for their lives in polished and lithe account of Mozart’s Requiem, with Zehetmair maintaining a perfect balance with the orchestra. The translucent layering of the rich fugal passages laid bare the inner dynamics of the work in all its glory. Andrew Foster-Williams’ rich bass-baritone savoured every syllable of the Tuba mirum, lingering wonderfully on the word sonum. Among the highlights from the chorus were a Rex tremendae hurled out with gusto, a sensitively modulated Lacrimosa and a graceful Agnus Dei. The whole was concluded with a thrilling Lux aeterna. It was a Requiem that would rank with the finest.