Zito (1-0) tossed his first shutout since April 18, 2003, not allowing a Rockies runner to reach third base. The Giants left-hander didn't issue a walk and fanned four in the dominating performance.
Sandoval's first-inning smash provided all the offense San Francisco would need in logging its first win of the young season after dropping three straight to Arizona.
Brandon Crawford contributed a three-run double and Hector Sanchez went 2-for-5 with an RBI single for the Giants, who spoiled the Rockies' home opener.
Colorado's Jhoulys Chacin (0-1) lasted only four innings, allowing four runs on four hits while surrendering five walks.
The game was interrupted for about 15 minutes before the fifth inning while a fan apparently hit by a foul ball was removed on a stretcher.
A motorized cart was driven onto the playing field from a left field gate at Coors Field to third base-area stands, where a stretcher was passed up into the crowd.
A fan was placed on the stretcher and driven back out through the gate as players and coaches watched.