This has been a topsy-turvy season at Old Trafford, where mounting injury problems have led Louis van Gaal to call upon on the club's academy products.
Fosu-Mensah and James Weir swelled the number of players handed a United debut this season to remarkable 14, with the pair coming off the bench to help secure a 3-2 win against Arsenal on Sunday.
It was an occasion to savour and one which has whetted Fosu-Mensah's appetite, with the versatile 18-year-old defender looking to build on his maiden appearance.
"I'm very happy - I just feel overwhelmed at the moment," he told the club's official website
"It was a big day for me but I have to keep working hard.
"It was really surreal
The players around me really helped but the most important thing is that the team played well and we did - we worked hard together.
"Arsenal are a big team, so we're delighted to win
It was a great performance."
Fosu-Mensah and Weir were amongst five United debutants over the last week alone, with Joe Riley's appearance in the FA Cup defeat of Shrewsbury followed by Regan Poole and Marcus Rashford featuring against FC Midtjylland.
It is no doubt who has made the biggest impact, though, with 18-year-old Rashford scoring an important Europa League brace and then another double to down Arsenal.
"I'm so happy for him," Fosu-Mensah said of Rashford.
"He's a very good friend of mine and it makes me happy every time he scores
Everyone works really hard at this club.
"It's great that young players are getting a chance - everyone knows the opportunities are there, so we're all working hard to take them."
Source : PA
Source: PA