FC Dallas's four-match unbeaten streak came to an abrupt end at the Home Depot Center as Los Angeles Galaxy cruised to a comfortable home win.
The hosts took the lead on 66 minutes when Jose Villarreal found Juninho on the edge of the six-yard box and the Brazilian slammed home.
David Beckham almost extended his side's advantage moments later, but he was denied from long range for the second time in the game by an impressive Kevin Hartman save.
Todd Dunivant wrapped up the points six minutes from time with a fierce left-footed shot from an acute angle.
Galaxy have now won their last three competitive games on home soil.