The game was initially delayed for an hour after heavy rain in Virginia forced the players off in the opening minutes.
Once play resumed, James McLean gave the Black Country outfit the lead when his dipping shot from 25 yards found the back of the net.
McManaman was in the thick of the action again after the break when his intended cross was headed off the line as the Baggies tried to convert their chances into a comfortable lead.
They were punished five minutes from time when Nate Shiffman netted an equaliser for the United Soccer League outfit.
However, West Brom secured victory in the dying moments thanks to Ideye's bullet header from a pinpoint Stephane Sessegnon's cross.