Chelsea defeated the Major League Soccer side 1-0 at the Home Depot Center in Carson, California with John Terry netting the decisive strike just after half-time.
Former England captain David Beckham made a brief debut for the American side, coming off the bench with 13 minutes remaining.
Dutch international Robben, whose contract talks have stalled at Stamford Bridge, was not included in the squad to face the Galaxy, prompting speculation he is about to sign for Real.
"Robben is injured," Mourinho said, referring to the knock on the winger's knee. "He's here and he's flying home with us, not to Madrid."
Meanwhile, Mourinho was impressed with the way the Galaxy had played in the friendly and suggested the other players in Frank Yallop's team had been trying to prove a point or too in the wake of criticism in the English media that Beckham was joining a 'pub team'.
"The game was difficult. I think LA played with a lot of class. I think maybe they wanted to show David that they have a team, maybe they wanted to show because it was an opponent such as Chelsea, at that level," Mourinho said. "Maybe it was because it was sold out, I don't know.
"But they gave us a hard game. The result could have been different because we had the chance to score many goals but at this moment in pre-season I prefer matches with difficulties than easy matches.
"They played against us with belief, with big concentration and defensively very well but I'm happy with the game. We won the match as we wanted to do. We played for about an hour in 4-4-2, which is a method I want to use.
"We played for the last half an hour with three defenders which was an experience I wanted them to have because during the season we'll have some matches where we must play like this.
"We finished this part of pre-season without any major injuries, only the one with (Wayne) Bridge, but after that no injuries and I go to London very happy."