It took the Sounders just eight minutes to open the scoring as an unmarked Obafemi Martins broke the deadlock by flicking a Mauro Rosales free kick into the upper corner with his back to goal.
The home side doubled its advantage 14 minutes later when Brad Evans chipped a ball over the top of the FC Dallas defense. Eddie Johnson latched on to the delivery to find himself one-on-one with Raul Fernandez, and the United States international slotted home with ease.
Seattle held the two-goal lead until the dying minutes when David Ferreira pushed Lamar Neagle in the penalty area, allowing Evans to seal the win with a goal from the spot.
Dallas (8-6-8) has not scored a goal since the seventh minute of stoppage time in its 2-2 draw with the Philadelphia Union on June 29. The club has managed just two points since to slide out to sixth place in the Western Conference with 32 points on the season.
Seattle (9-7-4) is unbeaten in its last three league matches and figures to be even stronger with the addition of Clint Dempsey.
08/04 00:39:05 ET