With three minutes gone, the England midfielder's long cross was met by Ely Allen, who scored with a crisp left-foot volley. Sydney FC equalised three minutes before halftime through Brendan Renaud, who let fly when a left-foot strike from 30 yards that evaded goalkeeper Steve Cronin.
"It is always good at pre-season to get games in," said Beckham. "You can do all the training you want but your match fitness that comes from games is important."
Beckham provided the spark for what would be the Galaxy's winner just before half-time.
His low cross was fumbled by Sydney goalkeeper Ivan Necevski, and Josh Tudela was on hand to turn the ball into the net.
"The right foot seems to be working," Beckham added.
"That is what I do, I get into positions and deliver balls that can help my team-mates and the strikers.
"I like having assists and tonight I was lucky enough to get two so it was a good night."