Midfielder Simon Dawkins, on loan from Premier League club Tottenham, was left free to fire home a 25-yard thunderbolt into Michael Gspurning's top left corner inside two minutes.
Schmid, who saw his side drop a four-game home winning run, felt the goal should never have been created by the Quakes as his Sounders too easily lost control when in possession in midfield.
"I thought we should not have gotten stuck with the ball right in front of our bench. We had talked about not letting Dawkins get the ball to his right foot, but we gave him a chance to run and he hit a great shot," said the Soudners boss.
"It was a goal that should not have happened, because we shouldn't have gotten stuck with the ball and lost it, but we should have reacted better once we did."
The Sounders levelled in the 14th minute when former Arsenal youth Steve Zakuani scored his first goal in 17 months after returning from a badly broken leg but the Quakes went 11 points clear at the top of Western Conference table when Chris Wondolowski netted his 22nd of the season with a glanced finish from Victor Bernardez's fierce cross on the half-hour mark.