Keane opened the scoring in the 45th minute when defender Todd Dunivant headed the ball across the goalmouth to Keane, who beat DC United goalkeeper Joe Willis.
Keane scored again in the 69th minute when Landon Donovan took the ball from United midfielder Branko Boskovic in midfield and then raced up field before playing the ball to Keane, who fired it past Willis.
After losing in the Champions League to Toronto FC and dropping its MLS season opener, Keane was happy to help the Galaxy get a win.
''In the games that we've played, we've outplayed teams, there's no question about that. But the teams have scored more than we had. That's the reason that we've lost,'' Keane said.
''We've had chances to win, but we haven't taken them. Today we took our chances and I think that the way that we've played for 85 minutes, we controlled the game. We played very well.''
Prior to their match, the Galaxy handed out their championship rings from their MLS Cup victory.
The ceremony was a new experience for midfielder David Beckham and Keane, who had their first exposure to the tradition.
''I've always got medals and trophies in the past so to receive a ring is special,'' Beckham said.
''Last season was a special time. We had come very close in the last three years, so to do it the way that we did it last year in our home stadium was special so to get the ring was even more so.''
But will the English soccer star wear the ring around town?
''At times I'm sure,'' he said. ''It's a big ring so it'll go someplace in the house with the rest of the medals and trophies that I've won over the years.''
Marcelo Sarvas made it 3-0 when he scored his first MLS goal in the 86th minute.
United scored just a minute later when Nick DeLeon added a goal from close range.
Although the United fell to 0-2 on the season, coach Ben Olsen was encouraged by his team's performance in their second consecutive defeat.
''There are signs of improvement, we just have to keep improving,'' Olsen said. ''I'm concerned after 0-2, no one wants to be 0-2 and have to deal with this, but we're moving forward and we'll get things sorted out.''
The Galaxy are now off until March 31.
''It's tough way to start the year, now we get a little reprieve to catch our breath a little,'' Landon Donovan said.
''First and foremost is to rest and then second is to get on the field on work on things. You kind underestimate that part of it, I know we're all pros and there is a lot of experience here, but there are a few guys who have never played together and we need that chance start gelling.''
- Robbie Keane
- Los Angeles Galaxy
- Landon Donovan
- DC United