Brad Evans (83rd minute) and Sammy Ochoa (88th) also scored for the Sounders, who will go for an unprecedented fourth straight Open Cup title when they visit Sporting Kansas City on Aug. 8.
"We'll be very aware when we step on the field in Kansas City that we have a chance to something that nobody has done," Schmid said. "You look at what these guys have done in one-off games, and you look at the history of any league around the world, and you don't see any team winning four straight FA Cups or Copa Del Reys."
Sporting earned its spot in the final on Wednesday with a 2-0 road victory against the Philadelphia Union.
Second-half sub Cesar Romero scored on a rebound of his own shot early in the 74th minute for Chivas USA. The Goats were seeking their first spot in the final, but lost to the Sounders in the semis for the second time in three years.
"Teams might win four league championships in a row, but because there are so many things that can go wrong in a one-off game, it's tough to win four (cups) in a row," said Schmid, who won the 2001 Open Cup with the Los Angeles Galaxy in addition to his three with Seattle.
Seattle, which has scored 15 times in four Open Cup games this season, has not lost a Cup game since joining Major League Soccer in 2009, putting together a 17-0-1 record. That includes title game victories at D.C. United in 2009, and at home against Columbus in 2010 and Chicago in 2011.
"Just the chance isn't good enough for us," said Evans, who has been with the Sounders since their first season, but didn't play in the first two Cup finals. "So we have to go into it and want this."