RSL entered the weekend one point back of leaders FC Dallas. But after Dallas was held to a 2-2 draw with Sporting Kansas City, Salt Lake seized its opportunity and moved one point clear at the top with goals from Kyle Beckerman and Robbie Findley.
The first half was a fairly tight affair with neither side stepping forward and grabbing control.
But the hosts made the most of a free kick in the 41st minute when Javier Morales struck the ball against the wall, redirecting it into the path of Beckerman, whose volley hit the underside of the crossbar and settle into the net.
It was one of the few chances in the first half for either side, but it didn't take the home side long to double the lead as the second goal came in the opening minute of the second half.
Findley got behind the Seattle defense and had his shot saved, but Alvaro Saborio followed up the play and returned the ball to Findley, who slid it past Sounders goalkeeper Michael Gspurning.
Seattle seemed to be out of ideas in the attacking third for much of the night, while Salt Lake almost added to the lead as Nat Borchers found the net in the 68th minute, only for the goal to be called back for offsides.
Saborio also had a good chance in the 87th but he nodded the ball wide from six yards.
The defeat ends a good run of form for Seattle, which had won five of its previous six matches.
06/22 23:32:13 ET