Jordan Morris scored the only goal of the match as Seattle Sounders advanced to the MLS Cup final for the first time in their history at the expense of Colorado Rapids, who lost 1-0.
Leading 2-1 heading into the second leg of the Western Conference Championship tie, Morris made sure of Seattle's spot in the MLS decider in the second half of Sunday's trip to Colorado.
The Sounders were out of form and out of sorts when long-serving head coach Sigi Schmid departed the club in July, languishing in ninth position mid-season.
But Morris completed Seattle's remarkable turnaround under Brian Schmetzer 11 minutes after the interval, receiving a throughball from team-mate Nelson Valdez and lofting his effort over onrushing Rapids goalkeeper Zac MacMath at Dick's Sporting Good Park.
The Rapids, who finished second in the west during the regular season - 10 points clear of the Sounders - pushed forward in search of two goals, but they were not forthcoming as Seattle emerged triumphant.
Awaiting the Sounders in the MLS Cup final on December 10 will be the winner of Montreal Impact and Toronto FC.
Toronto host Montreal in their all-Canadian affair on Wednesday, trailing 3-2.