Paul McGuinness' side drew level through Joe Riley early in the second period, only for the visitors to reclaim the lead and then defend it solidly for the final 22 minutes of the match.
Newcastle, wearing a Brazil-style away kit, arguably mastered the difficult conditions better than their hosts, producing some flowing football at times to put Paul McGuinness' boys on the back foot. Both of their strikes, in the 36th and 68th minutes, were created on the left flank by winger Rolando Aarons. For the first one, he cut inside and fired across Reds keeper Dean Henderson himself; for the second goal, he pulled the ball back for striker Adam Armstrong to plant home the winner.
Riley's equaliser, meanwhile, was a close-range conversion after the Magpies failed to clear their lines in the 54th minute.
Seemingly all kinds of weather, from sunshine to hail, were experienced at the Aon Training Complex. At one stage, the presence of lightning prompted the referee in the Under-16s match on an adjacent pitch to take the teams off as a precaution.
United: Henderson; Evans (Redmond 73), McConnell, Borthwick-Jackson, Thompson; Goss, Riley, Willock, Rashford (McTominay 81), Harrop; Mitchell. Subs not used: Ioannou, J.Pereira, Barber, Croskery.