Daniel Harding was due to conduct this performance of Mahler 3, but had injured his wrist. Robert Treviño, a rising young American conductor, and one with a burgeoning reputation in Mahler, was the late replacement and making his debut with the London Symphony Orchestra. It must be quite a challenge for even the most gifted young conductor to stand before one the world’s best orchestras for the first time. Then too there is London’s fabled parsimony with rehearsal time, and an audience with many a seasoned Mahlerian who has heard Solti, Abbado, Tennstedt and their successors play this composer in this city. And the small task at hand? Lead us all though the longest work in the symphonic repertoire, Mahler’s Third. Surely a seat-of-the-pants run-through lay ahead.

No-one needed to worry. Many a Mahler-lover has some misgivings about the Third, especially its often 35-40 minute first movement (called Part I). But from the opening pantheistic fanfare from eight horns we were in the hands of someone who believes in this extraordinary piece, and had something to say about it. Treviño was unembarrassed by the phantasmagorical events of the introduction, and relished the primeval woodwind gurglings and bass drum rumblings, the solemn intonations from gruff trombones and of course the military strut as, in Mahler’s unpublished explanation, “Summer marches in”. Summer rather quick-marched in on this occasion, and the first movement was done in a sprightly 33 minutes.

Nor was there the traditional long pause before Mahler’s Part II (the remaining five movements) began. Treviño wanted to keep some momentum maybe, and present the whole gigantic work as a single great arc. The next two movements are both dewy-eyed nature pieces in Mahler’s folk-poetry derived Wunderhorn manner. The second movement Menuetto – Mahler said it represented ‘What the Flowers in the Meadow Tell me’ – was delicately phrased but never precious, and with some athletic string playing in its swifter moments, and fine solos from the leader Carmine Lauri and the first trumpet Philip Cobb (what musicians the LSO has on its front desks!) The third movement’s inspired flugelhorn solo was as nostalgic as ever, well-positioned off-stage – not too far, not too near – and perfectly phrased by Nicholas Betts, like a voice from the composer’s boyhood.

The fourth movement is the still centre and conscience of the symphony, unveiling the psychological meaning behind all the nature music. Mahler initially thought to name the whole work after Nietzsche’s book The Joyful Knowledge but it is Nietzsche’s Midnight Song from Thus Spoke Zarathustra that forms the text of this sombre song for contralto. Swedish contralto Anna Larsson has graced many a production of Wagner’s Ring cycle, and here she recalled her role as Erda, and was suitably dressed in inky black for her Midnight Song. Erda-like too was the way she glided noiselessly on to the scene as the last fortissimo climax sounded of the third movement, and in the powerfully portentous warning she uttered, not to the gods as in the Ring, but to all mankind; “Oh Mensch! Gib Acht!” (O Man! Take heed!). This is the stillest piece of music in all Mahler, and Treviño’s poise and Larsson’s rich voice cast a powerful and profound spell.

The presence of The Tiffin Boys’ Choir and the Ladies of the London Symphony Chorus made for a very crowded Barbican platform – the stalls were minus rows A and B to accommodate the huge complement of singers and players - but both groups brought their usual well-tuned and well-prepared contribution to the fifth movement setting of the Wunderhorn poem “Three angels were singing a sweet song”. The long Adagio finale then stole in, properly ruhevoll and empfunden (peaceful and deeply felt) as marked, and kept moving at a flowing tempo, hushed and holy – Mahler said it could have been called “What God tells me”. It was full of sentiment but quite unsentimental, and its final blazing D major apotheosis felt properly achieved, rather than merely arrived at.

This was something of a triumph for Treviño on his LSO debut. One noted many small things that suggested that even in a short time a relationship had begun with the players, such as the long and flexible trombone solo in the first movement, where Treviño did not direct Dudley Bright, but simply accompanied him. Not all the playing was perfect of course – some later wind chord entries were less than immaculate, perhaps as tiredness crept in towards the end of such a long and demanding piece. But overall this was a Mahler Third to savour. After the applause and solo bows, Treviño had to be slightly cajoled by the leader to take one of his own. He would surely be welcome to return as a guest conductor, and reasonably soon.