The Timbers Army is sure to be out in force for United’s game in Portland on Saturday night. (Steve Dykes/GETTY IMAGES)

Using general measures, D.C. United should defeat the Portland Timbers on Saturday night and continue to strengthen its postseason outlook.

United has won three straight while conceding one goal; the Timbers are winless in four in a row with eight goals allowed and are relying on a backup goalkeeper. United (15-10-5) is in a tight playoff race; Portland (7-15-8) is playing out the string.

Any calculations working in United’s favor, however, are neutralized by the Timbers’ most potent asset: Jeld-Wen Field.

There is the artificial turf, a surface United hasn’t had to navigate since an April game at New England. There are the boxy dimensions: 110 yards wide by 70 yards long, the smallest in the league. (RFK Stadium is 110 by 75, while some are 120 by 75.)

And there is the reliable sellout crowd, wrapped tightly around the field, lifting banners bigger than Fenway Park’s Green Monster, generating European-style fervor and celebrating goals to the buzz of mascot Timber Joey’s chainsaw slicing a log slab behind the north goal.

“When you’ve got 20,000 people chanting in unison and almost bleeding for the team, it’s a difficult place to play,” said United’s Mike Chabala, a reserve left back who played for the Timbers from July 2011 until last month. “You talk about the 12th man around the league, it’s arguably the hardest and most exciting place to play. Playing in that environment extracts the most out of players.”

Inspired by their supporters and comfortable on a compact surface, the Timbers are 7-4-4 at home and have beaten the top clubs in the Eastern Conference, Kansas City and Chicago, as well as Western-leading San Jose and bitter rival Seattle.

Away from the Rose City, however, they are terrible: 0-11-4 with nine goals scored and 32 allowed. Losses or ties at playoff contenders Seattle and Vancouver in October would render them the fifth team in MLS history with a winless away campaign.

Although United won in Portland last season and have a superior squad this year, the visitors are bracing for a rigorous test. “You can’t get lost in the atmosphere,” center back Brandon McDonald said.

Coach Ben Olsen has emphasized the need for synchronization and focus in the defensive effort.

“We’ve got to keep alert. Heads on a swivel,” he said. Vocal “communication isn’t enough because you really can’t hear each other. It’s one of those games where you’ve got to put the onus on yourself to make plays and cover each other . . . bailing a teammate out and going on instincts.”

The narrow field presents additional challenges. The time and space normally afforded to a player in possession evaporate quickly in Portland. Before departing west Thursday, United’s coaching staff conducted exercises designed to prepare players for immediate pressure and the danger of rapidly developing scoring opportunities.

“It’s a helter-skelter type of place to play,” Olsen said. “It’s a lot of fun. It’s somewhere you need to embrace because there are very few ambiances in the league that are similar to this one.”

With four games remaining and a five-point playoff cushion entering the weekend, United would put itself in excellent position by earning at least a tie in Portland and winning at last-place Toronto (5-18-7) next Saturday.

“We have to stay humble, stay hungry,” McDonald said. “By no means are we in the playoffs.”

United notes: Center back Emiliano Dudar remains sidelined with a bruised knee. . . . Left back Daniel Woolard, out since early August with a concussion, has resumed jogging. . . . With Timbers goalkeeper Donovan Ricketts recovering from a shoulder injury, Joe Bendik, 23, is likely to make his third MLS start.