Tharaud, London Philharmonic Orchestra and Chorus, Nézet-Séguin, Royal Festival Hall

If ever there were a week for London to celebrate Poulenc in the lamentably under-commemorated 50^th anniversary year of his death, this is it. Two major choral works and two fun concertos at last join the party. But if Figure Humaine and the Concerto for Two Pianos look like being well positioned in the BBC Symphony Orchestra’s Barbican programme on Saturday, Yannick Nézet-Séguin’s chosen two were the victims of his own success in Prokofiev interpretation.

The Seventh Symphony, chronologically the last in this programme of works circa 1950 to tie in with The Rest is Noise festival’s agenda, upstaged the hazier glow of the Poulenc Stabat Mater which followed in the sharp orchestral means the dying Prokofiev brought to convey heartbreaking nostalgia.

It started as one of Prokofiev’s many "musics for children" but certainly didn’t end up that way: what the C sharp minor opening conveys is a bleak older-and-wiser winter’s tale, to be softened by magical elements like a late Shakespeare romance. Just as in his performance of the Fifth Symphony at the Proms, quite the best and deepest I’ve ever heard in concert, Nézet-Séguin grasped the dark undertow of the surface-simple Seventh, the urgency with which more acid elements intrude, the enigmatic spangling of the supernatural childlike trot which rounds off the basic first-movement argument (and the symphony).

His fabulous instinct for the right late romantic rubato highlighted the connection with Prokofiev’s beloved Tchaikovsky and Rimsky-Korsakov; the luminous focus he always brings to instrumental colour made us register every subtle shift in the masterly orchestral palette, from piccolo down to cor anglais in the winds, the finest of trumpet writing down to the baleful intrusions of trombones and tuba.

It was a foregone conclusion, given Nézet-Séguin’s infinite sensitivity, that he’d opt for Prokofiev's original quiet ending

Warning signs were there in the second-movement waltz from the start: Cinderella meets the Beast, and only collapse can ensue with shades of Mahler's nightmare hurly-burly and Ravel’s La Valse. The short Andante espressivo is frail pathos personified: one great, simple melody – tellingly adapted from Prokofiev’s portrait of the innocent Tatyana in his incidental music for a stage adaptation of Pushkin’s Eugene Onegin – bewitchingly orchestrated in a variety of keys, interrupted only by a bit of whimsy which normally seems extraneous but was as purposeful in its martial threat as anything in Nézet-Séguin’s seamless interprtetation.

There couldn’t have been anyone in the packed and varied audience who didn’t respond to the momentum and vividness of Prokofive's last galop which, like its predecessors in the Fifth and Sixth Symphonies, starts off too jolly to last for long. It was a foregone conclusion, given Nézet-Séguin’s infinite sensitivity, that he’d opt for the original quiet ending. Prokofiev tacked on a few more bars of galop reprise in a gambit for much-needed Stalin Prize money, and did it brilliantly, but the mystery curtain is surely the right one.

The tune which began a hyper-melodious concert – tonality is welcome in a 1950s programme, but for once a peppering of iconoclastic dissonance might have kept us on our toes – could have been by Prokofiev, but Poulenc made it his own in the Piano Concerto he composed as a showpiece for himself and the Boston Symphony Orchestra. Truth to tell, the work feels more like a Sinfonietta with piano obbligato, or did in the hands of soloist Alexandre Tharaud (pictured right), surely a subtle, interior kind of artist who, despite his half-smiles, didn’t really project the insouciant moments. But like Stravinsky and Prokofiev, Poulenc is rarely just the "cheeky chappie" in such pieces that the Radio 3 platform introduction argued. Nézet-Séguin made sure the rhythms and colours under the movie melody of the central movement rendered it exquisite rather than kitsch, and though the final "Rondeau a la française" sounds like an intermezzo in the wrong place, its “Swanee” quotations were fun enough.

The Stabat Mater should have come next, not after the interval: Prokofiev’s total focus made the incensed hazes, the instant spiritual highs of Poulenc's approach to the poem of Mary mother of Christ at the foot of the cross feel a little too facile until the stunning conclusion. Poulenc’s orchestral textures are more selective than usual, his choral writing brilliant and mystical in turn, but the work left me only half-warmed. The London Philharmonic Chorus did well, despite flat sopranos at the start; quiet meditations and surprising blazes made their mark. Soloist Kate Royal was only half there in her soarings, no match for Elizabeth Watts who had so shone in the later, greater Gloria back in April. The voice  needs knocking into shape before Royal sings the Marschallin in Glyndebourne’s Rosenkavalier next year.

It’s interesting how, while Prokofiev was forced to depths by his ill-timed return to Stalin’s Soviet Union, Poulenc found them in a brush with mortality and a mystic experience. But the Stabat Mater, on this showing, is only halfway there. The profundity comes in waves in his operatic masterpiece Dialogues des Carmélites, the Gloria and the a cappella choral work Figure Humaine, which I still can’t wait to hear on Saturday.

• Listen to this concert for the next six days on the BBC Radio 3 iPlayer
• More about Yannick Nézet-Séguin's Prokofiev at the Proms on David Nice's blog, I'll Think of Something Later