Greg Reynolds (0-1) took the loss in his season debut for Cincinnati. Reynolds was charged with five runs on eight hits over five innings.
Corky Miller led the Reds with two RBI.
The Reds scored twice in the second inning to cut San Francisco's lead to 4-, but the best they could do afterward was score one run in the fifth inning to match the run the Giants scored in the top of the frame.
Although the game was played in San Francisco, the Giants were considered the visiting team because they were playing a make-up game for a July 4 contest in Cincinnati that was rained out. The Giants wore their away uniforms in the game and batted in the top of the inning.