Seattle (13-7-10) nailed down its fourth straight post-season appearance only after Vancouver's Camilo barely missed the net on a volley in stoppage time.
Jeff Parke came close to a winner for the Sounders in the 85th minute, but Whitecaps defender Lee Young-Pyo cleared his shot at the goal line.
Brad Knighton also made three stops for Vancouver (10-12-9).
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