Pontius blasted a left-footed shot past goalkeeper Milos Kocic from 20 yards out in the 55th minute for a 1-0 lead.
United (5-3-3) doubled the advantage in the 75th when substitute Salihi sent a volley inside the far post off Brandon McDonald's flicked header.
D.C. won for the third time in fourth outings.
Toronto (0-8-0), meanwhile, became the first MLS team to drop eight straight at the beginning of a season, eclipsing the 0-7-0 mark set by the 1999 Kansas City Wizards.
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