Vogelsong (13-7) scattered four hits, didn't issue a walk and struck out four for the Giants, who posted their sixth straight win over the Rockies.
The San Francisco right-hander stroked a two-out single in the third inning and Andres Torres coaxed a walk before Fontenot delivered his two-run triple, providing all the offense San Francisco would need.
Santiago Casilla got the game's final two outs to collect his sixth save of the season.
Rockies starter Jhoulys Chacin (11-14) allowed only the two runs on eight hits over seven innings, walking one and fanning three.
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