The final began in extraordinary fashion as Columbus Crew keeper Steve Clark was unable to control the ball properly, before firing his kick straight against Valeri who diverted the ball into the goal to give Portland an early lead.
Things soon got even worse for Columbus, as Wallace moved brilliantly in the box to meet a cross from Darlington Nagbe in order to head his side into a two-goal advantage after just seven minutes.
A thrilling opening to the deciding fixture still had more to give, though, as Crew battled in order to find a route back into the contest and they were soon rewarded when Portland stopper Adam Kwarasey flapped at a cross, which allowed Kei Kamara to scramble the ball home and make it 2-1.
An error-strewn opening soon simmered down as both sides gathered their composure, and a goalkeeper finally made the right sort of impression on 41 minutes when Clark beat away Fanendo Adi's effort to preserve Columbus' one-goal deficit at the break.
There were still signs of nerves even after the break and Lucas Melano missed a fine chance to restore the Timbers' two-goal lead, running on to Adi's flick-on, but he scuffed wide of Clark's goal early in the second period.
On the hour mark, Kamara almost scored at the same end as he did in the first half when his miscued headed clearance bounced off his own crossbar as Crew clung on for dear life.
Clark was once again the saviour for the hosts as he reproduced his heroics to keep out Nat Borchers's point-blank header as Portland looked determined to snatch a killer third, but they would not need it.