With the 54-year-old keen to rest key players for the Europa League final three days later, Mitchell was handed a chance to start at left-back and impressed with a diligent, energetic display.
He has since played every game for the Reserves and completed a loan move to Scottish side Hearts for the remainder of the season.
And Mitchell, reflecting on the 2-0 win, recalled how Mourinho helped him feel at ease ahead of the clash with Palace.
“It was special making my debut for the club against Crystal Palace,” he said. “The manager just brought me in and told me that, although every game is important, there was no pressure on me.”
“It was the end of the season and I really enjoyed it. Obviously I hoped it would lead to more opportunities at United but that hasn’t happened, so that’s why I was so keen to go out on loan.”
The main reason behind fielding such a youthful side was to protect key players ahead of Stockholm, but Mourinho’s widespread use of young players had a positive epiphenomenal effect for those that received a rare taste of senior football that day.
Josh Harrop, who opened the scoring that day, has since joined Preston North End. Timothy Fosu-Mensah is thriving at on loan Palace in the Premier League. Axel Tuanzebe and Scott McTominay, having enjoyed a run of games towards the end of last season, have maintained places in the first team squad, with the former potentially joining Aston Villa on loan this month.
Angel Gomes, making his debut aged just 16, has gone on to sign a new contract at the club and made his debut for the Under 23 side this week, while even Matty Willock, despite not playing that day, has gone on to receive minutes in the Eredivisie with Utrecht this season.
Mourinho may often be regarded as a scourge towards youth, but there is no doubt that he has advanced the careers of these promising young players.