Bruce Arena's men had shipped nine goals in their previous two matches - against Real Madrid and Seattle Sounders - however their backline looked rock-solid throughout today's LA derby.
The designated visitors netted their first of four after 27 minutes, courtesy of Robbie Keane.
Man-of-the-match Landon Donovan found Keane on the edge of the six-yard box and the Irishman produced the coolest of finishes to register his 10th goal of the MLS campaign.
Donovan then provided the pass that set up Juninho to double Galaxy's lead 19 minutes into the second half.
The former Brazil international gave Chivas keeper Dan Kennedy no chance as his lashed home a trademark long shot into the top right corner.
The duo combined again 10 minutes later as Juninho flicked home Donovan's low cross from close range.
Donovan claimed his fourth assist seven minutes from time, crossing for Omar Gonzalez to complete the rout with a well-placed header.
David Beckham did not feature for Galaxy, as he was in London for the closing ceremony of the Olympic Games.