Patrick Nyarko led the way with a goal and an assist as the Fire edged closer to the playoff spots.
Chicago took an early lead through Patrick Nyarko. The winger grabbed a goal in the ninth minute when poor marking left him all alone to collect Joel Lindpere's cross and beat Zac MacMath.
Sheanon Williams equalized for the Union in the 60th minute, barreling into in a free kick from Sebastien Le Toux and guiding it home.
Mike Magee restored Chicago's lead in the 75th. Unmarked at the far post, he received Patrick Nyarko's pass and maneuvered around a desperate MacMath to find the net.