Paul McGuinness fielded a particularly youthful defence and the Royals took only seven minutes to break through when Lewis Collins blasted his finish past Dean Henderson.
A killer second strike arrived a minute before half time as Amadu Waritay profited from some neat wing-play to tuck a coolly-taken effort into the bottom corner of the net.
Captain Demetri Mitchell had mustered the Reds' best efforts but it was Jordan Thompson who reduced the deficit from the penalty spot with 18 minutes left on the clock.
United spurned numerous chances to complete a comeback to ensure a long trip back north after a frustrating time in Berkshire.
United: Henderson; Scott (Dearnley 68), Williams, Tuanzebe, Borthwick-Jackson; Riley, Kehinde, Rashford, Thompson, Mitchell; Croskery (Warren 77). Subs not used: Dorrington, Rathbone, Johnson.
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