No lead is ever safe for the Portland Timbers.
After dominating for most of the match, the No. 3 seed Portland Timbers remained tied with No. 6 seed FC Dallas with less than 10 minutes remaining in regulation.
Then, the breakthrough happened.
Diego Valeri found a cutting Jorge Villafaña who one-touched the ball into the top and back of the net past FC Dallas goalkeeper Jimmy Maurer in the 82nd minute.
That looked to be the game-winner, but it was not due to another stoppage-time gaffe by the Portland defense, who allowed an equalizing goal off a goal kick in the 93rd minute.
17-year old Ricardo Pepi originally hit the post before securing the rebound to keep FC Dallas' season alive.
It was the 15th goal given up by Portland this season after the 75th minute.
With the goal, the game went into extra time per MLS Cup Playoff rules in a knockout match.
Neither team found the back of the net, but Valeri hit the post on the final touch before heading into penalty kicks.
In the end, Portland outshot FC Dallas 22-12 with eight shots on goal compared to Dallas' five. The Timbers also had 55% possession after 120 minutes of soccer.
In penalty kicks, after each team converted its first seven attempts, Jorge Villafaña missed Portland's eighth attempt to lose the match.
It was the third-longest penalty shootout in MLS history.
FC Dallas will play either Seattle or LAFC in the Western Conference Semifinals.