A scoreless first half that saw little in the way of scoring chances was finally brought to life in the 65th minute by Adi's first goal, which he followed in the 71st with another to extend Portland's unbeaten streak to six games.
Chivas mustered little in attack and slumped to its fourth defeat in six fixtures, leaving the Goats on the bottom of the Western Conference.
Portland managed to put three shots on target in the opening 45 minutes but none of them seriously troubled Chivas goalkeeper Dan Kennedy.
The home side failed to test Portland goalkeeper Donovan Ricketts, and they found themselves behind midway through the second half when former Chivas man Jorge Villafana whipped in a first-time cross that Adi finished off to put the Timbers in front.
Diego Valeri came off the bench for Portland and made a quick impact by playing Adi in on goal, where he rounded Kennedy and rolled home his second goal in six minutes.
Chivas almost managed a goal in the 79th when a cross deflected off of Portland defender Rauwshan McKenzie and struck the post, but things only got worse in the 84th as Chivas finished the game with 10 man after Bobby Burling received a straight red card for a poor tackle on Adi.