Both sides were restricted to long-range efforts for most of the first half, but a great chance for Chivas was wasted in the 35th minute when Eric Avila fired over from just 12 yards out.
Avila was inches away from breaking the deadlock once again just after the break, with a free kick wide of the post with Donovan Ricketts looking helpless.
Portland were ahead in the 65th minute, when Adi lost his marker inside the box to open his account for the club by converting Jorge Villafana's inviting cross.
Adi doubled his tally just six minutes later by collecting Diego Valeri's defence-splitting pass, before taking the ball past Kennedy and tapping into an empty net.
Chivas pushed for a way back into the match in the closing stages, and were agonisingly close to pulling a goal back when Portland defender Rauwshan McKenzie inadvertently struck the ball against his own post.
The home side finished the game disappointingly as Bobby Burling was dismissed for a late tackle on Adi, who proved to be the match winner for the Timbers.