The contest seemed headed for a draw when a centering pass by Seattle's Zach Scott bounded off defender Segares for the decisive tally.
Lamar Neagle also scored for the second-place Sounders (14-8-4), who trail Western Conference-leading Real Salt Lake by two points with two games in hand.
Mike Magee scored his league-leading 15th goal for Chicago (10-11-5).
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