Fredy Montero came off the bench to score his second and third goals of the 2012 season. Cordell Cato, 19, picked up his first career assist.
The win is Seattle's fifth in a row, meaning the team continues a franchise-best start to the season with a 7-1-1 record. Dallas hasn't won in a five-game stretch, and missed Daniel Hernandez and Blas Perez through suspension.
In the opening half, Mauro Rosales and Scott Sealy both had shots which found post rather than net. Montero showed tidier finishing in the 68th minute with a powerful near-post blast. Two minutes later his diving header connected with a low deflected cross to seal the match.
Brek Shea came off the bench between the goals, still clearly not fully fit, and added one of Dallas' 15 total shots. Rookie Byran Meredith pulled off five stops to keep his second straight clean sheet.
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