Jimmy Medranda also scored for the Sounders, who remain the lone undefeated team in the league.
Medranda tied the score in the 71st minute following a corner kick. Joao Paulo's kick deflected off Fredy Montero and back toward the top of the penalty box, with Medranda running onto the ball and blistering a left-footed shot from 18 yards out under diving Vancouver goalkeeper Maxime Crepeau.
Ruidiaz gave Seattle a 1-0 halftime lead on a goal in the 40th minute, taking a cross from Brad Smith on the left wing and scoring with a left-footed shot from about 10 yards out. The play started when
The Sounders hadn't allowed a goal during the run of play all season until Vancouver struck twice in a seven-minute span early in the second half to take a 2-1 lead.
Dajome got the first in the 49th minute, taking a long through ball from Caio Alexandre and lifting the ball over onrushing Seattle goalie Stefan Cleveland just outside the top of the 18-yard box before regaining possession and putting the ball into an empty net.
The Whitecaps' second goal, in the 56th minute, also came on a Seattle defensive miscue. Dajome's cross for Cavallini bounced just over the head of defender Shane O'Neill. Cavallini didn't quite get all of a header from the top of the 6-yard box, but the ball trickled off his leg and rolled just inside the right post.