Kemp's blast off a fastball from Juan Gutierrez (0-5) ended a marathon pitching duel.
John Ely started for the Dodgers and pitched a strong seven innings, yielding just two hits and two walks with five strikeouts. But it was Jeff Weaver (3-1) who got the win after hurling a scoreless top half of the 10th.
The win was the third straight for the Dodgers and seventh decision in eight games over Arizona this year.
Diamondbacks starter Dan Haren fanned seven and allowed seven hits in eight scoreless innings.