Major League Soccer's Rivalry Week is getting a sequel in the Western Conference semifinals.

Sporting Kansas City and Real Salt Lake have quite a history, but nothing matches that of the Portland Timbers and Seattle Sounders.

The Timbers and Sounders have met more than 100 times in all competitions, dating back to 1975 in the old North American Soccer League.

The Cascadia Cup rivals will play the first leg of their two-game series Sunday in Portland. The second leg is scheduled for Nov. 8 at Seattle.

"It's going to be a final," Sounders midfielder Nicolas Lodeiro said. "They know us, and we know them, but each game is different. We have to be concentrated and play the full 90 minutes, 180 minutes.

"There's no tomorrow. If you lose this (series), you're done."

Since a 3-2 home loss to Portland on June 30, the Sounders have gone 15-2-2 to earn the No. 2 playoff seed in the conference and a first-round bye.

The fifth-seeded Timbers defeated host FC Dallas 2-1 in the elimination round Wednesday as Diego Valeri scored twice. The Timbers had to play most of the second half short-handed after defender Larrys Mabiala received a red card. That means Mabiala, who scored twice in Portland's June 30 win at Seattle, will have to sit out the Sunday match.

"This adds a little spice to the mix," Sounders coach Brian Schmetzer said of facing the Timbers. "We can't get it into a bar fight, but if it comes to a bar fight, we've got to be prepared.

"We want to go down to Portland and get a result. We want to come back to Seattle and defend our turf. We're going to go to win both games. That's the objective. We will not play just for a draw. We will go out and try to score. We understand the value of road goals."

The teams have met once before in the MLS playoffs, with Portland winning 5-3 on total goals in the 2013 Western Conference semifinals.

"Already, when you play them in the season, it's a special game," Timbers coach Giovanni Savarese said. "It brings (the game) to a different level. But now, in a playoff, in which only one (team) is going to go through, now there's a different component.

"We need to be very mature, which we are, and we are practicing with our feet on the ground, humble and ready to be able to give everything that we have in these two games coming up."

--Field Level Media

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