The Rose City took bragging rights with a vital win in the Western Conference semifinal first leg.
Portland took the lead in the 15th minute. Jack Jewsbury bombed down the right wing to latch onto a pass and whipped a cross in. Ryan Johnson exploded from seemingly nowhere to put a perfect header past Marcus Hahnemann at the near post.
Portland's second came in the 67th minute. A nice passing move found Kalif Alhassan on the right flank. He cut inside and picked out Darlington Nagbe's run across the box, and the Liberian took a lovely first touch to get away from Djimi Traore before finishing at the near post.
Clint Dempsey almost dragged Seattle back into the game late, but his header off a Mauro Roslaes corner kick bounced off the turf and tipped the crossbar as it went over.
Instead, Osvaldo Alonso was the one to make hand the Sounders a lifeline heading into the second leg. The midfielder rocketed a volley from the penalty spot after a long throw was flicked on by Shalrie Joseph.
The Sounders will have to overturn the deficit in Portland, where the Timbers have not lost since March, if they are to move on. Moreover, they'll have to do it without the services of Lamar Neagle, who picked up a second yellow card of the playoffs Saturday.