The Cascadia rivals meet for the second time in five days as the Sounders chase the Supporters' Shield and the Timbers grasp for playoff points.
The Sounders won Wednesday's Cup match 3-1, with Kenny Cooper and Marco Pappa scoring for the rave green in extra time following a Diego Chara red card. Osvaldo Alonso's opener had been matched by Darlington Nagbe's late strike to give the visitors hope before everything came crashing down.
It was the latest in a series of exciting clashes between the teams, following the 4-4 draw at Providence Park earlier in the season. Clint Dempsey, who had a hat trick in that meeting, should make his return for the Sounders from World Cup and late-night television duties.
Chara will be missing for the Timbers through a suspension, although this ban is based on yellow card accumulation, rather than Wednesday's ejection.
The Sounders are currently riding high with the best record in MLS: 35 points from an impressive 11-4-2 record. Although last week's loss to Vancouver cost them a three-game winning streak, it was just their second defeat since March.
The Timbers are not nearly so secure in the table. After 18 games, a 4-5-9 record sees Caleb Porter's side in seventh place in the West, chasing teams with better records and, for the most part, games in hand.