Craig Mitchelldyer/Portland Timbers

With their position in the Western Conference playoff picture under serious and immediate threat, the Portland Timbers will play their biggest game since MLS Cup 2015 on Sunday afternoon as they face the arch rival Seattle Sounders at Providence Park (2:00 PM, TV on ESPN).

Last weekend in Seattle, the Sounders β€” undefeated in five since firing manager Sigi Schmid β€” flew past the Timbers on the strength of three second half goals. Seattle now trails Portland by just a single point in the Western Conference table, with this β€” the rubber match between the two sides β€” likely to set the tone for the rest of the season.

The History

The Timbers didn't play particularly badly last Sunday at CenturyLink Field, but the defeat they went down to felt ominous for several reasons β€” the mysterious absence of Fanendo Adi from the starting lineup, several high profile defensive blunders, and the feeling that Seattle is suddenly verging on unstoppable.

Not that Portland should despair. Seattle has lost their last two games at Providence Park by a combined score of 7-2, with a 3-1 drubbing in July helping push Schmid out the door. Still, the pressure β€” only amplified by the MLS scheduling decision to have these teams meet in consecutive weeks β€” is on. Seattle would move ahead of Portland in the playoff race with a win.

The only real precedent for back-to-back meetings like this was when the two teams met in the 2013 playoffs. The Timbers won that series, taking the first leg 2-1 in Seattle and going ahead 3-0 in the second leg in Portland before holding on to win 3-2 and 5-3 on aggregate.

Jon Champion will be back in Portland to call the game for ESPN. On his only other visit to Providence Park, three weeks ago, the Timbers got one of the best wins of the season over Sporting Kansas City. Plenty of eyes, as always, will be trained on the tifo display from the Timbers Army β€” especially after last weekend's pitiful effort from the Emerald City Supporters.

The Tactics

The only surprise in the Timbers' lineup last Sunday was Jack McInerney starting up top in place of Adi, due, allegedly, to Adi's having missed the team flight to Seattle. Porter said midweek that all parties are moving forward, and Adi should be in the starting lineup this weekend. Lord knows the Timbers missed him.

And this week, it will be Seattle missing an integral piece. Clint Dempsey, perhaps more than any other player the lynchpin of this rivalry, is undergoing tests for an irregular heartbeat. He won't play on Sunday, and won't be involved with the US national team in September.

This will be Seattle's third consecutive trip to Portland that Dempsey hasn't played part in β€” but more than that, his is a situation that puts the game itself into perspective. If Sounders manager Brian Schmetzer doesn't want to change formation, the hapless Nelson Valdez is Dempsey's most likely replacement.

Steven Taylor wasn't particularly good in his Timbers debut last week, but Caleb Porter doesn't have any other good options at center back and Taylor's pedigree will buy him time to settle. Ditto for Vytas, who has been good going forward, but a defensive liability so far at left back.

Portland did get some good news on the injury front this week. Zarek Valentin and Ben Zemanski will be back available for selection, and Darren Mattocks looks likely to join them. None of the trio, however, are probable starters. Behind Adi, barring a formation change, we should see the same team that lost last weekend.

Chad Marshall, Joevin Jones, Christian Roldan, Andreas Ivanschitz, and Jordan Morris were all rested by the Sounders for their Wednesday night game in Houston. One star who wasn't rested β€” DP playmaker Nicolas Lodeiro β€” scored a 94th minute goal to salvage a 1-1 draw against the Dynamo and keep Seattle's unbeaten streak alive.

The tactical battle on Sunday will be fascinating to watch. The Timbers played two very different halves at CenturyLink last weekend, sitting in the first half, playing more proactively β€” and eventually getting punished β€” in the second.

Portland has to get Diego Valeri more involved than he was last weekend, and Adi's holdup play should help with that. Seattle, meanwhile, found most of their joy attacking Vytas last weekend. Defensive help from the left sided winger β€” most likely Nagbe β€” will be key. The Sounders also have a mismatch with Jordan Morris' speed against Ridgewell and Taylor. There should be plenty of goals in the game.

The Lineup

90 - Gleeson
2 - Powell
24 - Ridgewell (C)
27 - S. Taylor
5 - Vytas
21 - Chara
13 - Jewsbury
6 - Nagbe
8 - Valeri
26 - Melano
9 - Adi

The Pick

The Timbers know exactly how important this game is. They'll come out hot, and, with Adi back in the team, have the weapons to do damage offensively. It's hard to know how the Dempsey situation will effect Seattle, but coming off of the game in Houston, winning in Portland would be a big ask. 2-1 Timbers.