However, the Timbers were level within 10 minute as Ryan Johnson turned the ball in from close range after the home side quickly took a free kick and Darlington Nagbe hit a pinpoint pass for the striker to tap home.
Los Angeles almost retook the lead in the 35th minute but Omar Gonzalez hit the post with a close-range header after latching onto Sean Franklin's cross. Minutes later Ricketts made a fine save to deny Juninho from a free kick.
After the half-time interval, Galaxy keeper Carlo Cudicini made a great double save first to deny Nagbe's low effort and the former Tottenham Hotspur man quickly sprung to his feet to turn Johnson's shot on the rebound wide.
At the other end Ricketts made another great save to keep the scores level as Gyasi Zardes raided into the box, but the keeper made the stop low to his right with his feet.
Just as the game looked to be heading for a draw, Baptiste headed home Diego Valeri's cross past Cudicini in the 94th minute to earn his side all three points.