Mipo Odubeko scored his third of the tournament in a challenging SuperCupNI Globe semi-final.
Goals from Brandon Williams and Millen Baars gave United a deserved victory in front of over 2,200 people.
The under-16s reached the quarter-finals while FC Barcelona beat the under-12s.
Both the under-16 and under-12 sides progressed into the MIC quarter-final having already topped their groups.
United played four games at Arsenal's Hale End academy training ground, beating Bayern Munich and Juventus.