Arenado then lined a 2-2 pitch into left-center field, easily scoring Rutledge with the walk-off game-winner.
Michael Cuddyer drove in Colorado's other run with a first-inning single.
Giants starter Matt Cain settled for a no-decision after allowing just one run on three hits over eight innings. He issued one walk and struck out five.
Buster Posey drove in the only run for reeling San Francisco, which dropped a sixth straight.
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