The 2011 title-winners made it two in a row - and four franchise MLS Cups - when they produced a come-from-behind 3-1victory at the Home Depot Center on Saturday night.
Calen Carr put the Dynamo ahead on the stroke of half-time with a neat finish after a nice run from Adam Moffat's through ball before Omar Gonzalez equalized with a strong header from Juninho's hung-up cross on the hour.
The Galaxy were on their way to defending their title when skipper Donovan converted from the penalty spot five minutes after the leveler, due to a Ricardo Clark handball, and the MLS Cup was safe in the hands of the Los Angeles club when Robbie Keane also slotted home his spot-kick in injury-time, this time the penalty coming from interference from Dynamo keeper Tally Hall.
The Galaxy twice had the ball in the back of the net only for the goals to be disallowed, one for Keane being offside when he fired home after a corner, before the former Tottenham man produced a brilliant finish with his back to goal but Gonzalez was called for a questionable foul when heading down to his teammate.
It was the perfect way for Beckham, who has called time on his career with the Galaxy, to bow out whilst club legend Donovan is set to decide his future sometime down the track with suggestions he too could also depart the Carson club.