Jorge Perlazza and Eric Brunner added goals for Portland. Playing aggressively and backed by its usual boisterous crowd, the Timbers peppered Galaxy goalkeeper Josh Saunders with 15 shots. In contrast, Landon Donovan and the Galaxy barely caused Portland keeper Troy Perkins to break a sweat, with the majority of their seven shots on goal coming in the final 10 minutes.
The league-leading Galaxy were attempting to tie a franchise record with their 15th straight game without a loss. L.A. crushed Vancouver 4-0 on Saturday and David Beckham was returning after serving a one-game suspension for yellow card accumulation.
The stage did not seem to be set for an upset. The expansion Timbers had been reeling with just one win in their last 10 matches and entered the match having gone 0-4-2 at Jeld-Wen Field since May.
The news got worse before the game when it was announced that captain and center midfielder Jack Jewsbury was out with a strained hamstring, and that forward Eddie Johnson was suffering from a concussion.
The Timbers electrified the home crowd when Chabala, picked up July 22 in a swap with Houston, punched one into the back of the net from the left side in the 26th minute. That goal was followed in the 33rd minute by a blast from Jorge Perlazza.
It did not help. In the 68th minute, Brunner took a corner kick from Sal Zizzo and headed it past Saunders, sending the Portland crowd into a furious ''Beat L.A.!'' chant that lasted for several minutes.