Two goals from Charlie McNeill sandwiched a brilliant strike from Alejandro Garnacho as United comfortably secured a spot in the FA Youth Cup final, for the first time since 2011.
First-team skipper Maguire was in attendance at Old Trafford, alongside team-mate Dean Henderson, as well as senior club figures John Murtough and Darren Fletcher.
Before kick-off, Maguire spoke to the young Reds about a big night in their young careers.
“He was just saying good luck go and enjoy it, take it in,” Mather explained. “Because, obviously, we don’t know how many games we’re going to get to play at Old Trafford so, as a young lad doing it at such a young age, it’s such an amazing experience.