Sounders play Champions League quarters this week
The Sounders begin quarterfinal play at 7 p.m. Wednesday against Mexican club Santos Laguna.
Bragging rights are on the line, as the winner advances to the FIFA Club World Cup, where the Sounders could potentially play on the world stage.
"It's a really vital, crucial series, and we expect our fans to come out," said coach Sigi Schmid. "We'd love to see the place sell out."
The quarterfinals, semifinals and final are each two-game, aggregate-goals series, and away goals break a tie.
"This is the truest measure of North and Central American soccer," said Sounders midfielder Brad Evans.
If needed, extra time or a penalty-kick shootout will determine a winner.