A Sam Mather strike and two Gabriele Biancheri finishes either side of the break established a clear advantage for the young Reds and, after Emmanuel Osho netted to give the Royals hope, James Scanlon netted to seal the win for Travis Binnion's team.
Mather capitalised on an error from Reading keeper Tom Norcott and both Biancheri goals were well-worked moves from United but when Osho scored a deflected shot, it looked to give the hosts some momentum.
The young Reds remained composed and James Scanlon beat Norcott in added time, confirming three points on the road for our Under-21s.