The winning play came when Graham Zusi set up the onrushing Kamara, who fired a volley that fooled Toronto goalkeeper Milos Kocic and found the back of the net.
The score secured a third straight MLS win for Eastern Conference-leading Kansas City (14-7-4), which improved to 46 points.
Basement-dwelling Toronto (5-14-5), meanwhile, dropped its third in four matches.
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