Shostakovich. Cage. Ligeti. Bartók. Henry Cowell’s music brings them all to mind. If anything, Cowell’s relentlessly searching imagination set him on a path to historical perdition; Cage called him the “'open sesame' for new music in America”, and this idea that Cowell simply laid the groundwork for future developments has probably made his music into something of a footnote. Yet Cowell, to whom Bartók wrote asking if he might borrow the technique of cluster chords, composed some of the most visionary, passionate, and moving music of the American modernist movement. Nowhere is this better exemplified than in his 1928 Piano Concerto, given a stunning performance – the first at the Proms - by the indefatigable Jeremy Denk alongside Michael Tilson Thomas and the San Francisco Symphony, alongside the quirky Theme and Variations by Schoenberg, and Mahler’s magisterial First Symphony.

Denk seems to be more and more a presence in Britain these days. Having played chamber music with Joshua Bell earlier this year, he came fresh from a solo Prom on Monday apparently unaffected by the hair-raising demands of Scriabin, Beethoven and Bartók. Following a recording of Cowell’s Piano Concerto with this same orchestra and conductor, the group’s faith in the piece was obvious. Every moment felt exuberant; from the almost Emperor Concerto-like opening which alternates orchestral outbursts with percussive cadenzas featuring heavy use of the pianist’s whole forearm, to the affecting slow movement, combining the unique depth of sound clusters give with a lonely melody, this was real advocacy for Cowell’s style.

The slow movement opens with a lament for cor anglais, which is then passed, crushingly, to flutes playing a semitone apart, then goes round the orchestra accumulating notes until that lonely tune has become astonishingly expressive in its shattering harmonic crunch. Cowell’s use of clusters as expressive features is beguiling; hearing the expansion of the harmonic envelope deployed so naturally, particularly as it was played here, one could not help but think “Why had this never been done before?” After a whip-crack opening to the finale, some truly unique sounds emerge from the orchestra, given power by the unabashed dissonance that makes Cowell’s music sound so fresh. The piece ends with a screaming clash alongside another clustery piano chord that, with its massive voicing, actually joins the orchestra in an utterly uncompromising explosion of sound teetering just on the right edge of noise. As if that wasn’t enough, Denk gave a sublime encore performance of “The Alcotts” from Ives’s “Concord” Sonata.

Given they had engaged so convincingly with Cowell’s style, why did the SFS and Tilson Thomas remain so seemingly detached from Mahler’s, the symphony orchestra’s bread and butter? The First Symphony is certainly one of the greatest first symphonies ever written, full of youthful confidence, orchestral splendour and gorgeous melodies. Here though, it felt clinical, all the moments that keep this piece on programmes passed over in favour of an ‘architectural’ approach, hugely over-emphasising the music’s structure with heavy hands.

Before the jarring chord change that introduces the first appearance of the finale’s fanfare there was a 2-3 second gap; this is a moment of disjunction, but the harmony does that on its own. Once transitions had been made, the music tended to go along with little attention to detail; the Scherzo had no rustic stamp of feet, and the Ländler Trio was scarcely slower, the ingratiating elegance of the melodies lost. The slow movement’s klezmer interludes were characterless, and the songful, soulful middle section had no magic, no minute giving and taking of tempo to let the melodies really shine, a problem that reoccurred in the finale’s glowing slow interlude. Mahler’s glorious D major ending had no positivity, no distinction from the abortive attempt heard earlier.

Tilson Thomas’s details-first approach drew some admittedly beautiful playing from the SFS, though, with nary a technical error throughout. Principal horn Robert Ward was on fine form, the closing solo in the finale’s slow section full of nostalgia, and top marks to tuba Jeffrey Anderson and principal double bass Scott Pingel for excellent solos in the slow movement; Pingel’s double bass solo played with a particularly beautiful vibrato.

All this was preceded by a Schoenberg curiosity: his orchestration of the Theme and Variations Op.43 for band, rarely heard even in its original form. In a tonal style, it is characteristically pretentious, packed absolutely to the brim with contrapuntal detail and colour. Although Schoenberg didn’t consider it – not being a 12-tone piece – one of his ‘main’ works, there is much for an orchestra to get one’s teeth into, and Tilson Thomas’s very careful approach brought out as much detail and interest as one could want. It’s just a shame this sort of attention didn’t seem to be applied equally throughout the whole programme.