Eddie Johnson provided the winner as Seattle topped Portland on Clint Dempsey's home debut.
The goal came from a free kick won by Johnson after being slipped through by Lamar Neagle. Mauro Rosales provided the service and Johnson's glancing header found the corner for the only goal of the night.
The match was also the home debut for Clint Dempsey, and the crowd of 67,385 was the second largest for a stand-alone MLS match ever.
The win leaves the Sounders level on points with FC Dallas and ahead on the tiebreaker, moving the Sounders into the last playoff spot in the West with the club still holding at least two games in hand on the rest of the conference.