The Union struck first in the 40th minute when Philadelphia caught Chivas on a counter as Michael Farfan went around a Chivas defender firing in a cross that deflected off of defender Rauwshan McKenzie and onto the back heel of Adu for the goal.
Philadelphia finished the match with nine men as in the 75th minute when Union attacker Keon Daniel unleashed a hard challenge on Chivas' midfielder Ryan Smith, receiving a straight red.
Ten minutes later, Gabriel Farfan earned a red card for a late challenge on defender James Riley that led to an on the field scuffle.
Juan Pablo Angel made only his second appearance of this season in the 63rd minute after missing five games due to concussion symptoms.
