The 2014 MLS champions trailed by a goal at the break but produced a second-half blitz to kick off the season with an emphatic victory.
DC new boy Lamar Neagle opened the scoring in his first appearance for the club with a left-footed effort from outside the area which was placed past Dan Kennedy's left hand inside five minutes.
League debutant Daniel Steres levelled it up less than 10 minutes into the second half when heading home Mike Magee's corner from inside the six-yard box before the latter edged the Galaxy ahead.
Magee, upon his league return with the Galaxy who he last played for in 2013, neatly controlled a long ball from Sebastian Lletget before lofting it over DC keeper Andre Dykstra to out LA ahead on 64 minutes.
Less than 20 minutes later and the home side were two goals to the good courtesy of a well-taken penalty from captain Robbie Keane before Magee wrapped it up three minutes before regular time with a lovely glancing header from Steven Gerrard's flat free-kick.
It was a fantastic return for the 31-year-old who left the Galaxy for Chicago Fire in May 2013 and came off the bench at half-time to replace Giovani dos Santos and put in a Man of the Match performance for the Los Angeles club who immediately rise to the top of the standings on the Western Conference table.