PORTLAND, Ore. — Portland erased any lingering disappointment about last weekend's loss to Seattle by soundly beating the Sounders this weekend.

The Timbers scored four goals in the first half Sunday then held off their Cascadia rival 4-2, snapping the Sounders' five-game unbeaten streak.

"After the Seattle game we all hurt," said Steven Taylor, who had his first goal for Portland in the victory. "All week was tough."

Vytautas Andriuskevicius, Fanendo Adi, Lucas Melano and Taylor all scored for the defending MLS Cup champion Timbers (9-10-8). They remained in sixth place in the Western Conference.

Jordan Morris scored for the Sounders (9-13-4). They beat the Timbers 3-1 last Sunday in Seattle but then had a mid-week match at Houston that ended with a 1-all draw.

Seattle forward Clint Dempsey missed the game because of medical tests for an irregular heartbeat. Dempsey also was unavailable for the U.S. national team's upcoming World Cup qualifying matches.

"I will accept the blame for the first half. It's my job to make sure the team is prepared, and obviously that didn't happen," Sounders coach Brian Schmetzer said.

It was the third meeting this season between the Cascadia Cup rivals. Fans of the two teams, along with supporters of the Vancouver Whitecaps, created the Cascadia Cup in 2004 for the winner of the three-way contest based on points each season.

Portland won the first meeting with Seattle last month 3-1 and now lead the season series 2-1.

Andriuskevicius scored on a header off a corner kick for the Timbers in the 16th minute. Seattle goalkeeper Stefan Frei punched it up into the crossbar and it fell just inside the goal line.

Just some four minutes later Adi scored to make it 2-0. Frei saved a shot by Diego Valeri but the ball landed in front of Adi, who fed it into the goal behind the fallen keeper. It was Adi's 13th goal of the season.

Melano scored off Diego Chara's cross in the 29th minute, before Steven Taylor's header off a free kick in the 43rd to give the Timbers a 4-0 lead going into the break.

Seattle narrowed it when Andreas Ivanschitz's shot deflected off a Portland defender and past goalkeeper Jake Gleeson in the 47th minute. Morris scored some four minutes later with a header and the Sounders gained some momentum.

"I think it was the best performance of the year," Valeri said. "We knew that they'd played on Wednesday against Houston, they travelled, so we took advantage of that, and we did it well, with a good performance. We scored four goals, and it could have been more goals, too. "

The Timbers visit first-place Dallas next Sunday, still looking for their first road win. The Sounders visit San Jose on Sept. 10.

Seattle, in eighth place in the conference standings, could have been helped by Dempsey, who is tied for the team lead with eight goals.

"When you have one less attacker like that on the field, it always makes it a little bit tougher," Morris aid. "We were gelling, I thought, with Clint in the lineup, so it's tough. But, obviously, his health comes first and we hope Clint's good with that."

Seattle general manager Garth Lagerwey said Friday that Dempsey's irregular heartbeat is something the team has been monitoring during the season and the club is now waiting on the recommendations of doctors on how to proceed.

"Clint has given a great service to this club and we owe him an equal measure of respect and support as we go through this medical evaluation," Lagerwey said.

As a result, Dempsey was left off the U.S. national team roster for a pair of upcoming World Cup qualifying matches. The Americans visit St. Vincent and the Grenadines on Friday then hosts Trinidad and Tobago in Jacksonville, Florida, on Sept. 6.

But the Sounders have a representative on the team in 21-year-old Morris, who was named to the roster after missing out on the Copa America team.

Portland midfielder Darlington Nagbe also made the team announced by Jurgen Klinsmann. Nagbe has eight previous appearances with the national team.

The United States is second to Trinidad and Tobago in Group C. The top two teams advance to the six-nation CONCACAF finals, from which three automatically make the field for the 2018 World Cup in Russia.

If the U.S. wins on Friday and Trinidad beats Guatemala that day, the Americans will move on with one match left.