The first leg was all tied up at 2-2 but the Galaxy managed to get a 1-0 result in the return leg to send them through to the Western final where they will meet Houston Dynamo.
Goal hero Donovan said the result was enormous for the Galaxy but was keen to push on an clinch the MLS Cup.
"It's huge for our franchise," Donovan said. "Myself, Gordo (Alan Gordon), Cobi (Jones) ... we kind of understand what this all means. But we're not satisfied ... that's not good enough for us. Now we have a big opportunity to do something special.
"If you told me before the year we had a game at home against Houston to go to the MLS Cup Final I'd be excited. And I'm real excited for it."
Galaxy coach Bruce Arena was also delighted with the fact his side had was one win away from a chance at achieving glory.
"It's as special for me as the players and everybody else," Arena said.
"This has been one of my more enjoyable jobs in the last 30-35 years. I come in every day and these guys are a pleasure to work with. I think their vested interest in the team has made a difference.
"They lead, they get things right and they make my job a lot easier. This was a special game for those players, the things they did over the last six months to put the team in this position."