Van Slyke was sent to the plate with two outs to hit for pitcher Chris Withrow (3-0) and pounced on a 0-1 change-up from Josh Collmenter (4-3) to put an end to the contest.
A.J. Ellis had two hits and scored a pair of runs for Los Angeles. Yasiel Puig went hitless and struck out twice but also drew a walk and drove in a run with a ground out in the second inning.
Didi Gregorius hit a two-run homer for Arizona in the fifth inning to give Arizona a brief 3-2 lead that was erased in the bottom of the frame by a game-tying RBI double by Andre Ethier.