Stunned by two set-pieces, the first a magnificent free kick from Minnesota star Emanuel Reynoso, the second-seeded Sounders looked destined for an upset defeat before three goals in the last 15 minutes from Will Bruin, Raul Ruidiaz and Gustav Svensson turned the game on its head.
"I've said it before, I don't know how to say it differently: That's a locker room full of championship players," Schmetzer said after the match.
"It's easy to be successful and winning games, but when adversity hits, when you're socked in the jaw by Ozzie [former Sounders midfielder Osvaldo Alonso], Adrian Heath and Minnesota and you get back up and you persevere ... Minnesota had the game in their hand with 15 minutes go!
"In comes Will Bruin, and he sparks the group. I always talk about next man up, what's good about this franchise. Will's had his challenges, and he could be a starter, but he's here and works for his teammates.
"I couldn't be prouder of his response, of Gustav's response, Raul's goal. I'm telling you in that locker room, it's real.
"In my mind, that locker room -- not just the players -- the coaching staff, the medical staff, we've put ourselves in a great position to get to MLS Cup again. To win a game like that, as a soccer fan, that's an unbelievable performance. I don't know how we did it."
Playing in front of an empty Lumen Field due to coronavirus restrictions, Schmetzer lamented that such a win -- the Sounders' fourth Western Conference title in five years -- was secured without fans present.
"I wish that our fans were in the building to witness such a great Sounders victory," he said. "That was something we will talk about for many, many, many, many years to come about the history of our club. That was such a good performance by everyone.
"I haven't had a chance to soak it in. In our history, this will go down as one of our best games ever.
"We won MLS Cup last year, but this has to rank right up there."
Seattle will travel to Columbus to face the Crew in the MLS Cup final on Saturday.