Charlie McNeil’s 35th-minute goal was enough to secure the three points for the visitors, who fielded a number of their U23s regulars.
The young Reds, who welcomed the return of James Balagizi and Luca Stephenson from injury, pushed hard for a leveller in the U18s Premier League North encounter but were denied numerous times.
Marc Bridge-Wilkinson’s side looked bright in the opening 20 minutes of the contest.
U16s striker Ethan Ennis looked to break through clear on goal after being played in by Melkamu Frauendorf, only for United’s Will Fish to make a last-ditch challenge to thwart the danger.