With Wednesday's make-or-break Europa League final against Ajax looming large, Mourinho stuck to his word by resting numerous key players and handing four young prospects their full debut with sixth place already assured.
United manager José Mourinho promised after the0-0 draw with Southampton that the kids would be played against Sam Allardyce's side, with the Red Devils preparing for Wednesday's Europa League final with Ajax.
The Special One's tendency to to focus on neutralising their opponent rather than playing to their own strengths has undoubtedly instilled an inferiority complex in his Manchester United side and, should he approach the Europa League final against a young and ambitious Ajax side with a similar mindset, he could be severely punished. "It's the last game of the season and we were given a chance to impress".
And United impressed in a first-half performance that proved enough to secure a comfortable victory prior to their season-defining trip to Stockholm.
United's past successes in Europe have seen them lift the European Cup/Champions League on three occasions, most recently in 2008, and the European Cup Winners' Cup. 'I don't get that at all when people say he doesn't bring youth through.
Each of the young quartet fared well, with Harrop, 21, making a particularly strong impression by firing home a superb 15th-minute strike that was added to four minutes later by a Paul Pogba finish.
And Luka Milivojevic then had a free-kick saved by a stretching Pereira on his Premier League debut as United held on to a clean sheet. We will have time to think about different things afterwards.
"He was just saying be calm, be composed and go and play your normal game and enjoy it", he said.
"I have seen in the football media that certain pundits can not understand why our players are exhausted", he wrote ahead of the game at Old Trafford.
Herrera has shown his gratitude to Mourinho by repeatedly defending his manager in a hard season, with the run to the Europa League final and the League Cup triumph the saving graces of a campaign that has fallen well short of expectations.
I think I've had a good season, hopefully I can play more next season and be better. Josh Harrop, Demetri Mitchell, Joel Pereira and Scott McTominay - were then joined by 16-year-old Angel Gomes from the bench late on to offer a glimpse into United's future. They always help me and they make sure I improve all the time and get better each day.