Members of the Timber Army cheer during a May 6 game against Philadelphia. Portland has made the most of its raucous environs at Jeld-Wen Stadium, becoming the first expansion side in league history to win its first five home matches. (Jonathan Ferrey/GETTY IMAGES)

D.C. United has fled the early onset of summer in Washington for the enduring spring of the Pacific Northwest. The region’s cool, damp climate and casual nature is a welcome retreat from the East’s harsh heat and blinding bustle.

The tranquil backdrop, however, belies what United will encounter in its first match against the expansion Portland Timbers on Sunday at Jeld-Wen Field, a downtown den that has quickly become the most difficult stop on MLS’s seven-month tour.

Timber Joey, the lumberjack mascot, carries a chainsaw and, with each Portland goal, cuts a slab off a log to pass through the crowd. The Timber Army, a supporters’ group numbering 3,500 and awash in green, provides European rhythm with songs, flags and banners.

A roof, covering many of the 18,627 seats, contains the sound and spirit in the stadium, which dates to the 1920s and has undergone numerous renovations, most recently a $31 million facelift ahead of the club’s move from the second division to MLS.

“I’m excited,” United Coach Ben Olsen said. “I hope these guys take it as a treat to go in there in a wonderful atmosphere and try to spoil the party.”

The Timbers have made the most of their raucous environs, becoming the first expansion side in league history to win their first five home matches. With a 5-3-2 overall record, Portland entered the weekend tied for third in the Western Conference with 17 points, a tally that would’ve been even with the Eastern front-runners.

Timbers goalkeeper Troy Perkins, acquired from United in the offseason, described the home scene as “interesting and fun. There’s never a lull. Some places around the league, like Dallas, it’s pretty dead, especially for a Wednesday game. But here, we’re right downtown, people are coming straight from work and the city is into it.”

Unlike most expansion clubs, the Timbers had a fan base already in place. After playing in the North American Soccer League between 1975 and ’82, the Timbers played in lower-level leagues starting in 2001 before gaining entry into MLS. In 2010, average attendance was 10,727 — an astounding figure for a second-division organization.

With the Timbers in the top tier, the zest for soccer has intensified.

“Great audience, great atmosphere,” Frank de Boer, coach of Dutch champion Ajax, said Wednesday after defeating the Timbers, 2-0, in a sold-out exhibition. “I can see how a lot of teams have problems when they have to play here.”

The Timbers, riding a four-game unbeaten streak in league play, have made it difficult for visitors with a feisty style that reflects the personality of Scottish Coach John Spencer, a former MLS forward. They’ve taken advantage of a field that is a few yards narrower than most around the league and scored a majority of their goals off free kicks and corner kicks — “it’s no secret that has been one of our weaknesses,” United assistant coach Chad Ashton said.

The match reunites United with Perkins, who had two stints in Washington, and defender Rodney Wallace, a 2009 rookie of the year candidate who missed two-thirds of last season with a broken leg and was traded to Portland in November for United captain Dax McCarty.

Perkins said that, during United’s league-worst 2010 season, it “wasn’t a good environment.” But he added that “there’s no bad blood there. It was business. I haven't dwelled on it.”

Wallace, who starred at Bullis School and the University of Maryland, has started all 10 league matches this year. “It’s been a blessing to be a part of something completely different,” he said. “The atmosphere, it’s unbelievable. It doesn’t get any better, and it’s been a factor in our success.”

United (3-4-3) is unbeaten in three straight league matches but likely will be without leading scorer Charlie Davies (strained hamstring). Josh Wolff, the other starting forward, should be available after recovering from a groin injury.

After Sunday, United heads to Los Angeles for Friday’s match against a Galaxy squad that is 4-0-2 at home. Olsen has emphasized high concentration to avoid the defensive breakdowns that have plagued the club all spring.

“If we have that” in these two matches, Olsen said, “we can get four points [a victory and tie] out of it.”

United notes: Defender Dejan Jakovic will join Canada’s national team Monday for Gold Cup preparations and miss up to a month of MLS activity. . . .

Santino Quaranta (concussion) and Marc Burch (hamstring) didn’t travel with the team.