The Seattle Sounders got awarded a questionable penalty, but poured it on with three second-half goals against the Western Conference's second-place team.
A questionable penalty just before halftime gave the Sounders the lead. Aaron Maund's shoulder challenge on Lamar Neagle sent the Seattle forward to the turf inside the box and Gonzalo Pineda stepped up to bang home the spot kick and give his side a 1-0 lead at the break.
Marco Pappa made it 2-0 10 minutes into the second half with a glorious, bent free kick that crept into the side netting.
A quick counterattack in the 62nd made it 3-0. Obafemi Martins did some nice work to win a ball and set Neagle on his way. Once in the box he slipped a pass to Chad Barrett, who took it on first time to put the game out of reach.
Martins put even more gloss on the scoreline late on with a goal in the 90th as he tapped home a low cross from Kenny Cooper to make it 4-0.
The win gives the Sounders a five-point lead over RSL at the top of the Western Conference, with RSL holding a game in hand. The loss also snapped a streak of 12 straight matches to open the season without a loss.