The Union (12-10-10) had been trailing 1-0 for nearly the entire game before Brazilian midfielder Kleberson found him with a cross that he nodded past D.C. goalkeeper Bill Hamid for the equalizer.
The result allowed Philadelphia to run its unbeaten streak to three matches and move into the Eastern Conference's fifth and final playoff slot.
Nick DeLeon scored for United (3-22-7), which logged its 10th straight game without a win.
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