A questionable penalty call handed the Sounders a lifeline against the Whitecaps.
Chad Barrett got the scoring going in the 36th, picking his spot well with a header from a floated Kenny Cooper cross.
Erik Hurtado made sure the lead didn't last long. After being played through by Pedro Morales, Hurtado cut inside on Osvaldo Alonso before cutting a second time to leave both Alonso and Djimi Traore before smashing a shot into the Seattle net.
A 66th-minute Gershon Koffie goal, his first of the season, put Vancouver back in front. Stefan Frei chased a loose ball to the corner flag before clearing it, poorly, back into the middle of the park where Koffie was able to collect and hit from 40 yards into an empty net, making it 2-1 for the home side.
Seattle pulled back level in the 82nd when Jay DeMerit seemingly won a header in the Vancouver box, only to have it judged to be a foul as he climbed over Cam Weaver's back. Gonzalo Pineda calmly chipped the penalty home to make it 2-2.
The Sounders were nearly in the lead just over a minute later as Obafemi Martins banged a shot off the post, and the Whitecaps had a couple of late chances of their own, but neither side could find the winner.