Jeb Brovsky and Andrea Pisanu scored and Justin Mapp chipped in with a pair of assists for the Impact (12-7-6), who took over first place in the Eastern Conference.
Di Vaio's goals were his 14th and 15th of the season, giving him the MLS scoring lead.
Houston (10-8-7) gave up more than three goals for the first time this season but retained its hold on fifth in the East.
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