The Black and Red has one more chance to claim a road victory when it plays Friday against Sporting Kansas City.
Philadelphia scored in the 90th minute to prevent D.C. United from picking up their fourth win of the season.
Like Chicago, United is facing another desperate team with the Union on Saturday. But in addition to playing spoiler they're focused on picking up some points.
United (3-22-6) are now winless in their last nine league games and were unable to carry over any momentum from their US Open Cup win.