The Giants won their 15th straight with Zito on the mound, including the postseason. He hasn't lost since Aug. 2 against the New York Mets.
Facing constant criticism yet again for his girth, World Series MVP Pablo Sandoval made several nice stops at third and also ran down a foul popup to back Zito.
Zito blanked the Cardinals on three hits through the seventh. San Francisco's starters have gone 26 innings without surrendering an earned run so far.
Zito pitched a 5-0 victory in Game 5 of the NLCS at Busch Stadium that sent the series back to San Francisco, where the Giants won two more to reach the World Series. They went on to sweep the Detroit Tigers, with Zito winning the opener.
Zito began the year much like he did in his comeback season of 2012, when he pitched a shutout at Colorado.
The last time the Giants won 14 or more consecutive starts by a pitcher was Carl Hubbell's 16 straight from July 17-Sept. 30, 1936, according to STATS.
Fresh off San Francisco's second title in three years, manager Bruce Bochy carried the World Series trophy out from an entrance in center field as the first Giant announced to the cheering sellout crowd of 41,581.
The orange championship arrived by fire boat, with members of the San Francisco Fire Department handing it off to longtime fans to carry it the final way through the outfield.
After the 45-minute pregame ceremony, it was Zito's turn. By the time he was done with the 102-pitch gem, he walked off to chants of ''Barry! Barry!''
He allowed Jon Jay's leadoff single, then Carlos Beltran hit a hard grounder that Sandoval stopped to begin a double play - one of two turned by San Francisco.
Zito added a hit, too. He singled down the left-field line in his first at-bat to lead off the third.
Zito hopes to build on his 15-8 record last season that was his best since the former AL Cy Young award winner joined San Francisco on a $126 million, seven-year contract before the 2007 season.
For Cardinals manager Mike Matheny, a former Giants catcher himself, San Francisco's Game 7 clinching party in a downpour here is still plenty fresh.
''Coming back here is a good reminder of how things ended for us,'' he said.
The two clubs have captured the past three World Series championships - the Giants in 2010 and last year, the Cardinals in `11.
Westbrook, still two wins shy of 100, matched his career high with six walks and struck out one in 6 2-3 innings. Allen Craig had two of the Cardinals' hits.
Westbrook walked Gregor Blanco with one out in the fourth and allowed Brandon Crawford's single before Zito produced another timely bunt. He sacrificed and reached on Yadier Molina's fielding error to load the bases with one out. Westbrook walked Pagan for the run.
Zito had a perfectly executed bunt single to drive in a run during that Game 5 NLCS win.
Brandon Belt returned to the Giants lineup at first base after missing the final two games at Los Angeles with a stomach bug. Bochy went with the exact same lineup as Game 5 of the NLCS against the Cardinals.
On a day the Queen classic ''We Are the Champions'' blared through a near-empty ballpark as pregame warmups began, San Francisco started off a six-game homestand.
It will be a weekend of fanfare for the franchise. On Saturday, the team will honor NL MVP and batting champion Posey before the game with other former San Francisco MVPs, and Sunday will be the ring ceremony.
Sandoval and NLCS MVP Scutaro threw out a ceremonial first pitches.
NOTES: A moment of silence was held before the national anthem for late Cardinals Hall of Famer Stan Musial and victims from Sandy Hook Elementary School in Newtown, Conn. ... San Francisco has won 11 of its last 13 home openers. ... The Giants began a stretch with eight day games in their next 10. ... San Francisco sold out its 166th straight regular-season game dating to Oct. 1, 2010. ... The Giants are 11-3 in home openers in their 14-year-old ballpark.
Link to box score: San Francisco 1, St. Louis 0