Pianist Polina Leschenko gave a tantalising glimpse of what might have been in a scintillating partnership with Australian Chamber Orchestra and director Richard Tognetti playing Felix Mendelssohn’s Concerto for Violin and Piano in D minor at Perth Concert Hall on Wednesday. Tutti strings set a light, furtive tone in the opening as Leschenko waited patiently for her cue. Vigorous in the entry, she summoned the same force from Tognetti; the duo racing through scales, chasing across octaves. Quicksilver delivery from both then settled to a sonorous second figure, rhapsodic in violin while rumbling gently in piano. Renewed tutti attack triggered more gymnastics from the soloists; Leschenko’s feather-light touch mirrored in violin as Tognetti set his usual vigorous tempo. Drama rolled out in regular bursts from the keyboard as violin serenaded over the top; skittish fingerwork in harmonics highlighting concerted energy in piano. Virtuosic rivulets of sound died away to meditation and back, constantly changing through to a rousing conclusion. Syrupy strings led in the Adagio second movement, giving way to cool, lyrical piano. Tognetti joined in tentatively, mimicking Leschenko’s tone as the duo fell in and out of unison over tolling chords morphing to fluid, limpid runs. Tognetti was as ever on the qui vive, darting through the music, while Leschenko was almost languid, unhurried in her assurance with timeless ease in the cadence. The Allegro molto vivace finale returned to the furtive energy of the beginning, across the ensemble then in duet. For all the power of the Steinway, Leschenko never overstepped, giving space to the faintest stroke in violin then matching it with full ensemble; dynamic discipline a hallmark of her performance. Fierce in the robust conclusion, the soloists embraced before acknowledging sustained warm applause. Then the sad news. Leschenko was physically unable to attempt Chopin’s Concerto No.2, its dizzying demands so near and yet so far. Instead, Tognetti rolled out Vaughan Williams’ Lark Ascending. Complex chords underpinned the sylph-like solo’s opening moments as if a chorus of humming bees accompanied bird song, fading as the violin rose to fretful harmonics; Tognetti’s often feverish delivery tempered by the regret riven through this Great War lament. Broader harmonies backed up more generous tone in the mid range, with Tognetti’s crystalline flourishes answered in supporting lines. Rich tutti tones substituted for winds and horns as darker, funereal passages channelled tragedy before Tognetti rose again to the heights in infinitesimal harmonics triggering mellow harmonies in the lower register. Will’o’the whisp highlights in the solo again drove the action forward, punctuated by a single triangle. Multiple stopping lent extra heft to the violin, echoed with anthemic depth in the ensemble. Pealing lines of melody gradually settled back to the distemper of the opening and a reprise of the lark’s inexorable rise as Tognetti slid through the stratosphere with ethereal grace before dying away to a whisper and a rock star reception. Fanny Mendelssohn closed out the evening; her String Quartet in E flat major dawning in Romantic melodic lines, lush and emotive in the Adagio opening movement. Ebb and flow of dynamics and expression swirled around the ensemble, redolent of yearning. The Scherzo second movement broke out unannounced save for a telltale crouch and pounce from Tognetti, modelling the mood swing. Furtive energy again flowed around the stage, morphing to playful pizzicato then surging in cello and bass down to a pin-drop close. The Romanze third stanza returned to the dolorous quality of the Adagio opening, the happy homophonic ring of the all-string band working its mesmeric magic in cascades of sound over rock-solid cello and bass. Cascades of a different ilk launched the Allegro finale; a more open timbre than the Scherzo with feather-light touch in upper parts and a velvet tone to cello and bass, breaking to counterpoint with streaky flourishes in violins. An inverted pyramid of nine violins, three each of violas and cellos and one bass injected a bright, athletic quality to a rollicking climax. ACO returns in February with River, for Perth Festival.