The Galaxy's victory snapped an 11-game winning streak for the Dynamo (8-3-4).
The win was just the third this season for Los Angeles (3-3-9) and its second in nine games.
In the second half, Kamara had another chance to score when Brad Davis played him into the box. But Ricketts easily caught the poor chip.
The Galaxy mounted another threat in the 66th minute when Eddie Lewis drove a cross into the area for Edson Buddle, whose header skipped past the post.
Ricketts made his biggest save when he stopped Cam Weaver's shot from close range.
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