Camilo Sanvezzo netted twice from the penalty spot either side of half-time whilst Nizar Khalfan finished the job with two minutes remaining.
The first penalty for the Whitecaps came in the 43rd minute when RSL's Collen Warner was sent off for handling the ball in the area. Jay DeMerit's goalward header was knocked off target by a seated Warner who attempted to use his chest but part of his arm made contact with the ball and he was given his marching orders.
Camilo sent RSL keeper Nick Rimando the wrong way before adding a second less than ten minutes into the second half after Chris Schuler was adjudged to have handled the ball on the edge of the area.
After the match, RSL assistant coach Jeff Cassar said the club agreed with the penalty call on Warner but thought the red card was a bit much.
"We saw the review of it and it definitely hits Collen Warner's hand and I think the [PK] call is fine, a little bit debatable, but I think the red card ejection was a bit harsh," Cassar said.
"I talked to the fourth official and he said the referee though that Collen had intentionally did it, we feel differently, but that's how it goes."