Donovan helped put the Galaxy ahead in the 27th minute when he picked up a loose ball after a SKC turnover, got past defender Aurelien Collin and fed the ball to the middle, where Marcelo Sarvas flicked it into the net.
The LA star doubled the advantage in the 74th when Robbie Keane raced down an open field after Paulo Nagamura fell and moved it to Donovan, who blasted the ball into an empty net.
The Galaxy improved to 3-1-2 with the result.
Jimmy Nielsen made three saves for Eastern Conference-leading Kansas City (4-2-2).
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