SEATTLE (AP) Ryan Johnson flicked in a header early in the first half, and Darlington Nagbe scored midway through the second half on Saturday night as the Portland Timbers beat the Seattle Sounders 2-1 in the first leg of their Western Conference semifinals series.

The third-year Timbers, playing in their first MLS postseason contest, need just a draw in Wednesday's second leg at Portland to advance to the conference finals.

Osvaldo Alonso scored in the 90th minute for the Sounders, who need to win the second leg by at least two goals to win the aggregate total and advance.

If the Sounders outscore the Timbers by one goal in the second match to even the aggregate total, there would be overtime to decide the series.

Diego Chara started the play that led to Portland's first goal with a long pass toward the right side. Jack Jewsbury was on the receiving end and took it deep into the corner. He crossed it into the penalty area, and Johnson, cutting across goalkeeper Marcus Hahnemann's 6-yard box, flicked a header that went off Hahnemann's hands and into the far side of the net early in the 15th minute.

Johnson's goal was his 10th of the year for the Timbers, who went unbeaten through their last eight games of the regular season (5-0-3) to secure the West's No. 1 seed.

Nagbe made it 2-0 in the 67th minute. Kalif Alhassan, playing on the right side, sent the ball into the box. Nagbe spun around a Seattle defender and parked a shot past Hahnemann into the left side for his 10th of the year.

Alonso got one back for Seattle late after a long throw-in by Brad Evans was re-directed by Shalrie Joseph out to Alsonso, who drilled it in past Timbers goalkeeper Donovan Ricketts from 14 yards straight in front for his first of the season.

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The rivals have faced each other in the postseason three previous times, once in the NASL in 1975 and twice when the franchises were competing in the United Soccer Leagues in 2004 and '05. There have also been numerous meetings in U.S. Open Cup tournaments and memorable league matches, but nothing yet matching the stakes of the next 180 minutes between the two teams.

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Seattle's win over Colorado in the play-in game on Wednesday night was its first in seven games, a span that included a 1-0 loss in Portland. For the second straight match, Seattle used a diamond formation against the Rapids that appeared to accentuate the skills of midfielder Clint Dempsey and free space for forward Eddie Johnson. The formation change was successful against Los Angeles in the season finale and again against Colorado.

Portland closed the season by going unbeaten in eight straight games with five wins during the stretch. The strong close to the season vaulted the Timbers into the top spot in the Western Conference and put Portland in the position of having the advantage of playing the second-leg of the series at home. Porter downplayed the fact that this is Portland's first postseason appearance, noting that a number of his key players have playoff experience either with other MLS teams or playing in similar knockout tournaments in other parts of the world.

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The format is different with the two-leg series that does play into it. You can't just be locked on to the one game and understand how to approach the two together, Porter said. ... Collectively, we haven't been in this position but we have a lot of seasoned guys that have.

Aesthetically there was one drawback to Saturday night's tilt. Because the Seattle Seahawks play at home on Sunday, football lines were be painted on the field for Saturday's soccer match. With just 18 hours between kickoffs of the two games it was impossible to avoid having both sets of lines on the field.

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