Plata, the league's smallest player at 5-foot-2, assisted on Luis Gil's tally in the 47th minute with an accurate, bending cross following a long goal kick by RSL goalie Nick Rimando.
Twenty-four minutes later, the Ecuadoran midfielder assisted on an insurance tally when he got the ball to Javier Morales, who finished the play with a shot to the bottom left corner for Salt Lake (4-4-2).
Joe Cannon made a pair of saves for the Whitecaps (2-4-3), who remain winless after seven games.
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