Steele buried the winning goal in the 93rd minute to give RSL (6-3-1) its first triumph in four games.
Kyle Beckerman scored the game's first marker in the 7th minute and Salt Lake also benefited from an own-goal by Toronto's Richard Eckersley.
Eric Avila and Donell Henry tallied for TFC (0-7-0), which has tied the 1999 Kansas City Wizards for the worst start in MLS history.
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