A long-range strike from Uruguay international Nicolas Lodeiro and Raul Ruidiaz's brace sealed Seattle's first win in four attempts against LAFC.
The Banc of California Stadium certainly lived up to its reputation with an electric atmosphere in what was LAFC's first Western Conference Final in just their second season of existence.
Expectations were sky high heading into the game after Bob Bradley's side followed up a record breaking regular season, in which they claimed the Supporters Shield, by defeating local rivals LA Galaxy 5-3.
In a pulsating opening, Eduard Atuesta put a firecracker in the stands when his sumptuous long-range free-kick, won after some some mercurial play from ex-Arsenal and Real Sociedad winger Carlos Vela, sailed over the wall and dipped past Seattle goalkeeper Stefan Frei.
Chants were still ringing out around the stadium when Ruidiaz scored an equally stunning equaliser in front of the 3252 stand.
The Peru international left Eddie Segura for dead before rifling the ball into the top corner from just inside the box.
Four minutes later and Seattle were in the lead through Lodeiro, who fired home a precise strike from outside the box past an outstretched Tyler Miller.
Lodeiro turned provider for Ruidiaz's second after 64 minutes, with LAFC defence once again giving the 29-year-old far too much time to pick out where he would put the ball past Miller.
The Sounders players were jubilant after the game and immediately went over to the tiny green crowd tucked away in the corner who made the long journey down the West Coast to cheer them into the MLS Cup.