The hosts entered this contest in improved form, which translated to a start with encouraging moments, as they got the first shot off with Jarrod Bowen glancing his header wide from a fizzed Crysencio Summerville cross, shortly before the Dutchman saw a curling effort of his own palmed wide by Senne Lammens.
Michael Carrick’s side have also been on the up and asked questions from corners, with Harry Maguire heading wide before Luke Shaw’s effort from a low Bruno Fernandes delivery was cleared off the line by Aaron Wan-Bissaka.
Clear-cut opportunities came at a premium as the half progressed, though, as Axel Disasi stopped a Fernandes through ball from finding Casemiro before Diogo Dalot reached a Wan-Bissaka cross ahead of Taty Castellanos at the other end.
Dalot almost created problems for his own team when he overplayed in a potentially dangerous area, yet Amad Diallo hit the side netting from a tight angle moments later.
After a first half that had largely been played at a walking pace, the Hammers swiftly took the lead after the restart as Tomáš Souček played Bowen through and got into the box to guide his captain’s cross through Lammens’ legs.
Summerville blocked a Dalot strike as the visitors looked for an equaliser that they thought had come in the 63rd minute, when Casemiro headed home Kobbie Mainoo’s cross from deep but strayed agonisingly offside before doing so.
Bowen’s ambitious strike was deflected behind moments later, but the Red Devils soon went back on the front foot with substitute Šeško testing Mads Hermansen from range before Bryan Mbeumo headed a Shaw cross wide.
Souček then blocked Mbeumo’s curling attempt late on, and Joshua Zirkzee then glanced his header agonisingly wide as West Ham battled into the dying moments.
Even so, they ultimately suffered late heartbreak as Šeško expertly flicked Mbeumo’s cross into the top corner in the 96th minute, extending Manchester United’s unbeaten PL run to nine games to keep them fourth, albeit while seeing a four-game winning streak come to an end.
West Ham have still lost just one of their last six matches across all competitions, but are two points behind Nottingham Forest, having played one more game.
Flashscore Man of the Match: Tomáš Souček (West Ham United)