Rashford entered the fray just before the hour mark with the scores level and immediately changed the game, rounding off a superb run down the left hand side with a pin-point assist for Juan Mata after 63 minutes.
The youngster was deservedly handed the Man of the Match award by Sky Sports following what was a truly bombastic display out wide.
Mourinho, speaking to the BBC after the game, was quick to hail the 19-year-old.
“It made it difficult for us [West Ham going down to ten men], but more difficult for them,” he said.
Forty-eight hours is tough. It was hard for us to think well with one more man and it was very hard for them physically.
“Having Ibra this season and next season is excellent for Marcus.”
It is no secret that Rashford, more than any other player, embodies everything supporters want to see in a Man United player: fearless, devastatingly fast, indefatigable, always looking to burst forward.
United garnered their worldwide fame through being ruthless warriors, hellbent on not just winning but winning emphatically, battering opponents into submission. And this is exactly what Rashford did to right back Håvard Nordtveit – and indeed the entire West Ham back four – for thirty minutes at the Olympic stadium.