Substitute striker Kenny Cooper scored with his first touch to secure a 2-1 victory, as the Sounders came from a goal down with an hour gone against FC Dallas to secure the three points at CenturyLink Field in Seattle.
Michel Garbini Pereira gave Dallas the lead from the spot after 15 minutes but, inspired by the in-form Obafemi Martins, Seattle found a way back in the final half-hour with Lamar Neagle and Cooper scoring the goals.
The win was the Sounders' fifth straight and saw Sigi Schmid's men claim a five-point gap on the West's second-placed team, Real Salt Lake.
It was also the fifth time in their past six MLS fixtures that Seattle had come from behind to claim points.
Brad Evans' foul in the box on Dallas striker Blas Perez led to the visitors taking the lead in Seattle with Michel placing his penalty inside Stefan Frei's right-hand post.
The Sounders laid siege to Dallas' goal but had to wait until the 62nd minute to equalise with Clint Dempsey feeding Martins, whose cross was turned into the net at the near post by Neagle.
Martins, who had scored in Seattle's past three games, notched his sixth assist of the season in the 88th minute to help the hosts to victory, picking out Cooper from the left wing, and the American forward tapped the ball home from inside the six-yard box.
Seattle (22 points) have a comfortable lead in the Western Conference, although Real (17) have a game in hand, while Dallas (16) are third having played 10 games like the Sounders.
Colorado Rapids (15 points) missed the opportunity to overhaul Dallas as they could only manage a scoreless draw at San Jose Earthquakes.
In the other MLS game on Wednesday, a second-half header from Will Bruin saw Houston Dynamo triumph 1-0 over Columbus Crew to claim second in the Eastern Conference.
Houston (14 points) trail the East's leaders - Sporting Kansas City - on goal difference, while New England Revolution and New York Red Bulls are also on 14 in third and fourth respectively.
