Zito will face the Detroit Tigers' Justin Verlander in Wednesday's opener at AT&T Park.
Giants teammates credited Zito with turning around the team's fortunes in the National League Championship Series against the St. Louis Cardinals last week.
Trailing 3-games-to-1 and on the verge of elimination, the Giants got 7 2/3 shutout innings from the left-hander en route to a 5-0 victory to keep their season alive.
They went on to take two more from the defending world champions, claiming the 22nd NL pennant in their 129-year history.
The honor represents a major turnaround for Zito, who was kept off the Giants' post-season roster during their run to the 2010 World Series title due to a string of ineffective performances.