Findley set the tone with his first tally of the season when he emerged from a scrum and vaulted over prone Sounders goalkeeper Michael Gspurning to flick in a loose ball.
Luis Gil doubled the advantage in the 35th when his diving header on a cross from Ned Grabavoy gave RSL (2-2-1) a crucial insurance goal.
Brad Evans scored in the 57th for Seattle (0-3-1), which is still seeking its initial victory four games into the season.
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