Second half-substitute Darren Mattocks also scored to help the Whitecaps (6-3-2) win at home for the first time since early April.
Playing his first game in MLSoccer after arriving on loan last month, Techera was only on the field because fellow midfielder Mauro Rosales limped off with an injury in the 12th minute.
The Whitecaps made it 2-0 in the 44th when Rivero muscled Philadelphia defender Ethan White off a sloppy back pass before beating a helpless Sylvestre with a low shot for his sixth of the season.
Sylvestre got the start for Philadelphia (1-7-3), which has lost four in a row, after John McCarthy and Andre Blake went down with injuries in practice this week. A former member of the Whitecaps' youth system, Sylvestre was signed on a short-term loan from the Carolina RailHawks on Friday.
Mattocks subbed on for Rivero midway through the second half, then iced things with a superb individual effort for his third of the year.
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