Philadelphia (2-7-3) ended its five-game winless streak, while D.C. United (6-2-3), the Eastern Conference leader, had its eight-game undefeated streak stopped.
The Philadelphia Union will return home on Saturday as they welcome D.C. United to Chester.
The Union next plays at D.C. United, also of MLS.
Jack McInerney scored two goals before halftime to lead the Philadelphia Union to a 3-2 victory over D.C. United on Sunday.
Chris Pontius scored in the 78th minute to lift D.C. United to their fourth straight victory with a 1-0 win over the Philadelphia Union on Saturday night.
Sebastien Le Toux scored two first-half goals, Michael Farfan added the go-ahead goal in the 57th minute and the Philadelphia Union extended their unbeaten streak to five with a 3-2 victory over D.C. United on Thursday.