The game was the Sounders debut for star American forward Clint Dempsey. Dempsey was called in with 11 minutes remaining in the first half after starting forward Obafemi Martins was taken off following a tackle by Doneil Henry.
Dempsey, a former Fulham and Tottenham player, got his first touch a few minutes later in front of the Toronto goal, but defender Ashtone Morgan took him off the ball.
The other goal for the Sounders (10-7-4) came on an own goal by Henry.
Jonathan Osorio's fifth goal of the season early in the second half was the lone goal for Toronto (4-11-8).
Seattle's opening goal came in the 16th minute as it took advantage of some slack Toronto marking.
Eddie Johnson ran onto a cross from the left side and headed the ball across the goal where there were three green Seattle shirts waiting with no Toronto players in sight. Rosales had ample time to chase the ball, get his left foot on it and angle a shot past Joe Bendik.
Seattle doubled its advantage with five minutes remaining in the half when Lamar Neagle fed a cross in from the left side. Henry took a poke at the ball with his left foot, but could only redirect the ball toward his own goal. With Bendik wrong-footed, the ball rolled slowly into the goal.
Toronto had a strong start to open the second half. Osorio got Toronto back in it when he converted a quick passing play seconds after the opening.
After controlling a ball from the left side, Osorio had the presence of mind to round a defender and hit a left-footed shot just over the line before it was cleared by a Seattle defender.
Toronto continued to push and controlled much of the latter period of the game, but the closest it would come was in the 60th minute when substitute Robert Earnshaw had a left-footed shot from just outside the penalty area come back off the post.