TUKWILA, Wash. – For all the epic regular season and U.S. Open Cup battles between the Seattle Sounders and the Portland Timbers over the years, there’s precious little MLS postseason history to speak of.

The Cascadia foes have played just one playoff series in the MLS era – a 2013 Western Conference semifinals matchup that saw the Timbers romp to a 5-3 aggregate victory. But with Portland bagging a 2-1 Knockout Round road win over FC Dallas to open their Audi 2018 MLS Cup Playoffs campaign on Wednesday, the Sounders and Timbers will finally get a chance to add another postseason chapter, starting with a massive Leg 1 fixture at Providence Park on Sunday (5:30 pm ET | ESPN, ESPN Deportes, TSN 5, TVAS).

“This [matchup] adds a little spice to the mix,” Sounders coach Brian Schmetzer said at Friday's training session. “It’s going to be a mentally challenging match. The physicality, making sure calm heads prevail. We can’t get into a bar fight. But if it comes to a bar fight, we’ve got to be prepared. So, it’s an interesting opponent. I think the league does like it and I think the fans and everybody will be jazzed up.”

The Sounders are an entirely different unit than the one that bowed out to the Timbers in 2013, with midfielder Osvaldo Alonso representing the only Seattle player potentially involved in both series.

But Schmetzer was an assistant under former Seattle boss Sigi Schmid at the time and, famously, kept a photo of former Timbers head coach Caleb Porter celebrating that 2013 triumph on Seattle’s CenturyLink Field turf on his office desk as a source of motivation.

The Porter picture is gone now, but Schmetzer still remembers the sting of the defeat vividly. And while settling that score might not be his foremost motivation, the Sounders’ boss also said it’s not an outcome he’s interested in seeing play out again.

“That series hurt because we got outplayed,” Schmetzer said. “You have to credit Portland. They beat us fair and square. So I didn’t have much recourse other than keeping that [picture] as a reminder of what we could have done better.”

The Sounders downplayed the notion they’ll be approaching Sunday’s match differently than any other playoff opponent. But after Friday’s practice at Starfire Sports Complex, there was also a palpable sense that the high-stakes nature of the upcoming series is indeed enhanced by the opposition.

“I know there will be a lot of adrenaline, especially because it’s a playoff game,” striker Raul Ruidiaz said. “The games are more intense. At any moment, there could be difficult plays. We have to be intelligent and manage the game.’’

The key, midfielder Gustav Svensson said, could very well be weathering what figures to be an early storm from Portland — a famously potent counterattacking side, especially at home.

“I don’t think [the matchup] changes much for us, it changes a lot for the fans,” Svensson said. “We want to win this game, not only for ourselves, but for our fans as well. This game means a lot for the franchise, not only for the playoffs but because it’s our rivals.

“They’ll come out as hard as they can,” he added. “They’ll try, especially the first 15-20 minutes, they’ll come out with everything they have. So, it’s up to us to make sure we don’t give them too much in those 15-20 minutes.