Facing elimination from the playoffs, the Giants starter pitched 7 2/3 innings of shutout baseball, with six strikeouts to help San Francisco to a 5-0 victory.
The Cardinals still lead the series 3-2 but must now clinch it in San Francisco. Game Six will be on Sunday at 7pm ET.
Zito, the pitcher with an impressive contract but slightly less impressive statistics, also contributed to the Giants' offense, with an RBI bunt in the decisive fourth inning.
San Francisco scored four runs in the top of the fourth and forced Cardinals starting pitcher Lance Lynn out of the game.
Pablo Sandoval had two hits, two runs and an RBI for the Giants. The Cardinals outhit the Giants 7-6 but failed to make them count.
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