In a US soccer rivalry dating to 1975, this one is notable

FILE - In this April 26, 2015, file photo, Seattle Sounders' Clint Dempsey, left, celebrates after he scored a goal against Portland Timbers goalkeeper Adam Kwarasey, second from right, as Timbers' Alvas Powell, right, stands in the goal during the second half of an MLS soccer match in Seattle. The Timbers host the Sounders on Sunday in the 100th meeting between the two rivals from the Pacific Northwest. (AP Photo/Ted S. Warren, File)

PORTLAND, Ore. (AP) American soccer’s most storied rivalry reaches a milestone on Sunday.

That’s when the Seattle Sounders and the Portland Timbers play for the 100th time in a series that dates back to 1975, when both teams were part of the North American Soccer League. The rivalry persevered throughout the years until gaining national attention when the Timbers joined the Sounders in Major League Soccer in 2011.

Since both have played at the sport’s top level in the United States, Seattle has a 9-5-6 advantage in league games.

When MLS granted franchises to Portland and Vancouver, the league hoped to build on the regional rivalry already in place in the Pacific Northwest. The trio already played for the Cascadia Cup, a three-way competition based on points that was created by supporters of the teams in 2004, when they were all part of the USL.

But the rivalry between Portland and Seattle has been particularly heated, and it’s proven to be a success for MLS. Ticket demand and TV ratings are much greater for the matches. ESPN2 reported that viewership jumped 26 percent for a Timbers-Sounders match last year.

”Soccer is driven by intense rivalries, and the Sounders-Timbers rivalry is among the best in all of professional sports,” MLS Commissioner Don Garber said. ”Two great clubs, two stadiums packed with passionate fans – the rivalry between Seattle and Portland has been an important driver in the success of our league and has been a model for others that have followed. There’s really nothing quite like a Sounders-Timbers match.”

There have been some epic battles in the MLS era between the teams. Portland won the two-legged Western Conference semifinals against Seattle in 2013. The Timbers have further bragging rights because they won an MLS Cup first.

One note: Sunday’s match will not count toward the Cascadia Cup because this year the MLS schedule between the teams is unbalanced, so one of the games between the Timbers and the Sounders had to be thrown out.

TRASH TALKING: The Timbers mockumentary about the rivalry, which poked fun at everything from Seattle’s traffic to Sounders star Clint Dempsey’s rap video, found a fan in documentarian Ken Burns, who tweeted about the project.

”There are different levels of ”made my day” … having Ken Burns himself actually view this project rates among the highest,” Timbers owner Merritt Paulson responded on Twitter.

GUZMAN RETURNS?: Portland midfielder David Guzman could return from a knee injury on Sunday against the Sounders. The 28-year-old Costa Rican sprained his knee during international duty at the end of March, and the national team has been careful about his return because he’ll likely figure into the team’s World Cup plans.

SPEAKING OF THE WORLD CUP: In addition to a possible appearance by Guzman, Portland’s side includes Andy Polo, who could make Peru’s roster for soccer’s premier tournament. Seattle has three potential World Cup players: Nicolas Lodeiro (Uruguay), Gustav Svensson (Sweden) and Kim Kee-hee (South Korea).

Missing will be Sounders defender Roman Torres, who plays for Panama. Torres has a hamstring injury that is expected to sideline him with the Sounders for some four weeks and could put his chances of playing for his country at the World Cup in jeopardy.

The deadline for the 32 World Cup teams to announce preliminary rosters is Monday. The teams must be whittled to 23 players by June. 4.

WHERE PORTLAND’S AT: The Timbers got off to a rocky start this season under new coach Giovanni Savarese. They were winless in their first five matches, which were all played on the road because of the ongoing expansion project at Providence Park. But Portland has since won three straight, including last weekend’s 1-0 victory at San Jose.

”I think the unity has been much better. Everybody’s covering each other, everybody is working for each other,” Savarese said. ”They sacrifice defensively, and they believe offensively, so I think that’s the key factor so far.”

WHERE SEATTLE’S AT: The Sounders were struggling with just one victory in seven games to start the season, falling into last place in the Western Conference. But they got a big boost with a 2-1 victory against Toronto – their MLS Cup rivals – on the road Wednesday night.

”It’s massive,” coach Brian Schmetzer said. ”Toronto has been a good rival. I enjoy my chess matches with Greg (Vanney). I think he has done a great job with this club but now it is on to the next rival and that is a big one for us, a little closer to home, a little less travel time.”