Magee, obtained by the Fire in a May 24 trade with Los Angeles, notched his league-leading 14th tally of the season when he got a pass from Patrick Nyarko and sent a high shot over Union goalkeeper Zac MacMath, breaking a 1-1 deadlock.
Nyarko scored in the 9th minute for Chicago (8-9-4), which is battling for a playoff spot in the Eastern Conference.
Sheanon Williams scored in the 60th minute for the Union (9-7-7), who suffered their first home loss since May 15.
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