Seattle eventually sealed the all-important first-leg win 2-1 thanks to a stunning late Clint Dempsey free-kick to give the Sounders the advantage in the tie heading into next week’s second leg in Dallas.
But things didn’t start so well for the home side as Fabian Castillo fired FC Dallas in front after just 18 minutes. He latched on to a fine Mauro Diaz pass to finish, moments after Dempsey wanted a penalty at the other end.
Seattle pressed for an equaliser but couldn’t seem to beat Jesse Gonzalez in the Dallas goal. But Andreas Ivanschitz had other ideas as he fired life back into the Sounders on 67 minutes.
The Austrian midfielder beat three Dallas players before firing a sublime left-footed shot into the bottom right corner, sending the roof off of CenturyLink Field.
The atmosphere then ramped up and Seattle managed to complete their comeback when Dempsey fired a stunning free-kick into the top corner just four minutes from time.
Dallas will feel hard done by but they have what could prove to be a vital away goal and will now need to win the game at Toyota Stadium next Sunday night.
The two sides will meet in the second leg at 19:30 ET (00:30 GMT) next Sunday evening with a place in the conference final against either Portland or Vancouver up for grabs.
What did you make of the game in Seattle? Did the Sounders deserve the win?