The Canadians dominated the first half at Century Link Field and felt confident their ascendancy would translate into goals.
But it was Seattle who broke the deadlock nine minutes after the interval through Kelvin Leerdam.
However, in the build up to the Dutchman's deflected strike, Osorio was involved in an incident with Sounders counterpart Christian Roldan.
The Canada international took a heavy touch in the centre of midfield and Roldan stepped into front to cause a collision.
30 seconds later Leerdam's deflected strike would give Seattle the edge they needed before eventually winning the final 3-1.
Speaking to Tribalfootball after the game, Osorio wasn't pleased with the call.
He said: "Everybody knows what should've been called on that play. And it changed the game no question.
"I'm not going to sit here and say that its the reason we lost. But it changes the game. It's a crucial, crucial play. And in a final like it can change the game."
Asked about what the referee's opinion, Osorio continued: "That I ran into Roldan, that's the explanation."
Osorio added: "Yeah it hurts you know. It ends up being big play in the game and that's it. Theres nothing we can do. Somehow we're going to get over it, it happens.
"For their season they deserved to win the game with the way they finished. But we were in control, everybody in football knows this, and [that decision] changed the game."