After her electrifying Evita, Rachel Zegler is back at the Palladium – although not on its balcony – joining Ben Platt for a 25th-anniversary concert of Jason Robert Brown’s two-hander. A few nights earlier, Lily Allen was on this stage performing her blistering broadside West End Girl, about love turned sour. The Last Five Years has an equitable approach to its own curdled marriage as a couple give their perspectives through alternating solos. Its masterstroke is to have one of them chart the story in reverse, beginning wearily post-breakup, while the other goes chronologically from first infatuation. Halfway through they duet at their wedding.

Brown directs and conducts from the piano on a set by Bretta Gerecke that separates out the band on to various levels, with central staircases, evoking the apartments and urban spaces where the story unfolds. Novelist Jamie (Platt) and actor Cathy (Zegler) enter from opposite sides and meet in the middle for an embrace, foreshadowing the show’s midway union. Platt retreats, to a plangent string accompaniment, and Zegler sings her stark opener, Still Hurting, staring at the way he went. Absences are accentuated throughout the semi-staged production and Zegler painfully captures the frustration of a partner whose unfinished business goes unheard by a departed ex.

Platt bursts back on for his giddily comical, Latin-feel solo, Shiksa Goddess, as he anticipates his Jewish family’s reactions to his passion for the gentile Cathy. “My grandfather’s rolling, rolling in his grave,” he sings in mock-horror baritone while Zegler serves a more sardonic humour, flashing a fixed grin to a musical ping in See I’m Smiling. As the story charts Jamie’s meteoric rise, he is caught up in his own whirlwind – at one point leaping from spotlight to spotlight like they’re stepping stones. Meanwhile, Cathy – acting in summer stock, career stalling – watches on. Brown makes acute observations about partners sharing or shut out from each other’s success, belief in another and oneself, and the toll of professional rejection (including Cathy’s spiralling interior monologue during a number that frames Brown as the pianist at her audition).

Through it all is a deep understanding of how time passes. This is a musical measured in critical minutes, ambling evenings, late arrivals (her), early departures (him) and the reverie of artistic pursuit (what Cathy calls “Jamie-land”, as the author stares out of windows – which are positioned around the backdrop). Brown even gives us a talking clock, its ticking hands mimicked by Platt, as he performs Jamie’s short story The Schmuel Song, Mark Smith’s latticed lighting conjuring a deserted tailor’s shop. (Plays about artists often come undone when representing the characters’ art but Jamie’s talent is convincing; Cathy is given no such chance to shine.) The story captures the racing nature of your 20s and life running away from you. “I thought we had a little … time,” sings Cathy with resignation, realising there is none left.

Like a memory play, the format creates a jumble of joy and pain over an interval-free 90 minutes. Even playing at their most mournful, Brown’s eight-strong band (with a pair of especially fine cellists) can carry a sparkle like the residue of romance. There is rollicking piano, pop-cabaret fizz and a daffy high-kicking number performed by Zegler with a cuddly toy, but a jewellery-box fragility remains. Both actors go through a number of costume changes and appear in formal wedding outfits together for The Next 10 Minutes, performed with exquisite stillness.

Album recordings of the musical cleanly isolate Jamie and Cathy’s stories; on stage, the pair overlap a little more and have some extra scenes, slightly weakening the overall effect. It is a feat for actors who are barely together to convey a convincing bond but Platt and Zegler manage it even if you’re left with a sense of individual sadness rather than lamenting the end of their relationship itself.

A five-year romance is a long time, especially in your 20s, and while it may not be a Benjamin Button-level transformation, Zegler convincingly grows younger before our eyes and Platt loses his initial lightness. The casting of these musical-theatre megastars meant the show, which did not hold a press night, sold out at lightning speed. I spent hours chasing a ticket on fan-to-fan resale sites but it was time well spent.