United had their fate in their own hands knowing two victories here and at home to Bournemouth on Sunday would assure Champions League football next season.
Louis van Gaal's side arrived in control of their own destiny but with little margin for error on an emotionally charged evening at Upton Park.
It was typical of our misfiring season that the chance was squandered with a largely tepid and lifeless performance that was punctured only briefly by Tony Martial's brilliance.
United may have been affected by the trauma of the late arrival and the delaying of kick-off, but the first 45 minutes fell well short of what was expected and required given how high the stakes were.
It was only down to West Ham's profligacy that we were merely 1-0 down at the interval- there was no excuse for a tepid first half that lacked urgency, shape and organisation.
It was as if van Gaal had not impressed upon his players that a door to the Champions League that had looked shut for so long was not so much ajar as wide open, instead it looked like meaningless, end of season stuff.
The superb Martial offered hope - kills you, doesn't it- but we weren't good enough to make it count as the hosts scored twice in four minutes to once again reveal the flaws in this fragile United side.
For long spells this was performance that made us question how such an ordinary side could even be in contention for a top-four place.
True, we missed the aerial and physical presence of Marouane Fellaini - utilised to such success in the FA Cup replay - but this was a deserved defeat after a display that produced much of the evidence that has left so many United fans questioning the manager's future.
For four tantalising minutes, all seemed well for LVG- Martial's brilliance had turned the game, undeservedly on its balance, in favour of United and that coveted Champions League place was within sight.
At 2-1 ahead, we were 14 minutes from a win that could have offered the opportunity to put a different spin on the season.
It was not to be as old vulnerabilities resurfaced to leave Van Gaal back on the rack- the players had dragged their manager out of a hole then threw him back in again.
It has been obvious since Christmas that there has been no great appetite inside Old Trafford to replace Van Gaal: if we were certain he was not the man for the job, former Chelsea boss Mourinho would surely already be in office or least officially lined up.
Ed Woodward clearly wants his man to succeed and the FA Cup may offer salvation but there is no doubt a Cup win is a much harder sell than Champions League football.