Los Angeles could have doubled their lead in the 13th minute when Omar Gonzalez headed an effort at goal from a corner, but Nick LaBrocca was on hand to clear the ball off the line.
The Galaxy did get their second goal as Gordon flicked the ball to Gyasi Zardes inside the box, who laid a first-time pass to Baggio Husdic and the midfielder placed the ball into the bottom corner.
Zardes got a goal of his own just before the break with another neat move for the home side, as the striker peeled off his man and collected Donovan's pinpoint through-ball to slot an effort past Irwin.
In the second half, the Galaxy quickly got a fourth goal when Zardes was brought down in the box by Chris Klute after a scramble in the box and a spot kick was awarded. Donovan took the penalty and notched his second goal of the game with a cool finish.
Husidic almost got his second goal for the night when he latched on to Marcelo Sarvas's cross at the back post, but his volley clattered off the woodwork and went wide.
Los Angeles got their fifth goal of the game when Stefan Ishizaki lifted a cross into the box and Zardes rose highest to head home from six yards out.
The Galaxy completed the rout in the 86th minute with the third brace of the game, as Husidic got his second goal when he collected Donovan's pass on the edge of the area and drove his shot into the bottom corner.