Jimmy Nielsen recorded his league-leading 14th shutout for Sporting (17-7-7), which extended its unbeaten streak to nine matches. Sporting had not won against Chicago at home since a 3-2 victory on Aug. 22, 2007.
Chicago (16-8-7) had a four-match winning streak snapped and lost for just the second time in nine games.
Zusi put Sporting up 1-0 in the 11th minute and then scored in the 6th minute of second-half stoppage time.
Chicago manager Frank Klopas and Fire defender Gonzalo Segares were both ejected in second-half stoppage time, Klopas drawing a straight red card from referee Chris Penso and Segares picking up his second caution.