The national cup competition has been a source of much joy for the Sounders, who head back to the final yet again.
The Rave Green earned the right to take on the Philadelphia Union with a 6-0 demolition of the Chicago Fire, and are on the hunt for a fourth triumph in the competition. Seattle lifted the trophy three years running between 2009-11, but lost in their most recent final, bowing out to Sporting Kansas City on penalties in 2013.
Chad Barrett and Obafemi Martins both found the net for Seattle, and Andy Rose and Kenny Cooper each grabbed a brace as Chicago was ruthlessly exposed. Cooper also picked up a pair of assists in a man-of-the-match performance against the Windy City side.
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Seattle will now have to travel to PPL Park to face the Philadelphia Union on Sept. 16 in the final. If the Sounders manage to lift the Cup once more, they will tie Chicago for most wins all-time by an MLS Club.
"It's fantastic," said Seattle head coach Sigi Schmid after the game. "It's something we said to the club that we take seriously. As I said to Pappa and Jalil Anibaba before the game, 'This is the reason you came here - to battle for trophies - so show it tonight.' And that's what they did and both of them had good games.
"We won our first Open Cup on the road at DC and now we have to go into Philly and do it. It's going to be a long road trip, because we go from Philly to New York to Dallas, so we will be on the road for 10 days, it will feel like preseason.
"We will be ready for it, this is what we want to do. If you answer it, you try to win it."
Although Philadelphia has never won a trophy in its five years of existence, the region has a strong tradition in the Open Cup. Bethlehem Steel won the competition five times between 1914 and 1926, and the Philadelphia Ukranians won in 1960, '61, '63 and '66.