Reigning MLS Cup champion Seattle crushed FC Dallas 4-0 to climb into third place in the Western Conference.
In Seattle, the Sounders took a 31st-minute lead through Victor Rodriguez, who finished clinically after being put in by Clint Dempsey.
A quick-fire brace from Will Bruin helped Seattle on their way, the forward putting away a rebound and later a side-footed finish. Lamar Neagle headed in a Nicolas Lodeiro cross to complete the comfortable win in additional time.
Portland cruised past D.C. thanks to a second-half brace from Sebastian Blanco at Providence Park. Diego Valeri scored via a penalty before Alvas Powell curled in a fine effort shortly after halftime.
Blanco made it 3-0 with a curling strike into the top corner on the hour mark before he sealed the victory with one more insurance goal.
Kansas City and Houston are also heading to the playoffs after playing out a 0-0 draw.
The first-place Vancouver Whitecaps were held to a 1-1 draw by the San Jose Earthquakes, who are fighting for the sixth and final spot. Yordy Reyna gave Vancouver a first-half lead before Chris Wondolowski equalized with 13 minutes remaining.
Nemanja Nikolic pulled clear atop the goalscoring charts with a hat trick in Chicago Fire's 3-2 win over the Philadelphia Union, who scored off an Alejandro Bedoya strike and Johan Kappelhof own goal.