Zito, without whom the Giants might not have earned the World Series championship banner that they raised before Friday's game, surrendered three hits in seven innings to help San Francisco outlast St. Louis, 1-0.
The Giants won their 15th game in a row that Zito pitched, dating back to last year and including the postseason. Yet he downplayed the streak in summarizing his performance.
"It's not conducive to being in the present with every pitch," he said.
Despite allowing only one Cardinal to reach second base, Zito called his experience "a grind. There were a lot of pitches I would have liked to have back."
Zito furnished one of San Francisco's most critical victories last October by blanking the Cardinals for 7 2/3 innings in the Giants' 5-0 triumph in Game 5 of the National League Championship Series.
But Zito didn't use that victory as a template for this one.
"It's hard to look at a game three or four months ago and have that affect the game today," he said.
Due to his pregame obligation to warm up, Zito couldn't revel in the championship flag-raising ceremony that others found stirring.
"We all had chills and goosebumps," Giants manager Bruce Bochy said. "I think some guys had tears."
Watching Zito work proved inspiring for the Giants, whose starting pitchers have not permitted an earned run in 26 innings this season. The Giants and the 1976 Milwaukee Brewers are the only teams since 1916 whose starters went the season's first four games without yielding an earned run.
Zito retired 15 of 17 batters beginning with the first inning's final out. The Cardinals then launched their only semblance of a rally as Allen Craig singled and advanced on Matt Carpenter's two-out walk in the seventh. Zito responded by retiring Pete Kozma on a fly ball.
Zito received ample defensive assistance.
"It seems like it goes hand in hand with good pitching," Bochy said.
Third baseman Pablo Sandoval was particularly impressive, starting a pair of double plays and assisting on five putouts overall, mostly by ranging or diving to his left.
"Third base is a key position when I'm throwing, because I throw off-speed stuff to get guys out front," Zito said. "Pablo's always ready over there. He picked me up huge today."
Zito still did most of the heavy lifting. Two of his fellow left-handers comprehended his artistry on the mound.
"What he's really developed in the last two years is the ability to go in and out with the off-speed stuff," Javier Lopez said.
Lopez explained that left-handed pitchers are taught to work right-handed pitchers low and outside. But Zito, said Lopez, doesn't rely only on this tactic.
"When he's really locked in, he's able to start locating inside, not only with the fastball, but throwing the cutter in on the hands, regardless of velocity," Lopez said. "That's what you tend to appreciate because there's never a predictable sequence for him and that's the best part about his game."
Jeremy Affeldt, who worked a perfect eighth inning to set up Sergio Romo's third save in as many games, observed that Zito understands his skills and can command his variety of pitches more thoroughly.
"He pitches with the stuff that he's got," Affeldt said. "I think there was a little bit of a learning curve for him."
Citing Zito's repertoire consisting of a curveball, sinking fastball, changeup and a cut fastball, Affeldt added, "He's going to mix it up and he's never going to throw the same speed twice. It's an add-and-subtract game. Guys can't really get a certain speed off him, so it's hard to guess with him."
Said St. Louis' Yadier Molina, "We couldn't catch up to anything," which isn't what hitters usually say about pitchers such as Zito who lack overpowering velocity.
Catcher Buster Posey paid tribute to Zito's intelligence.
"He has a great game plan going into every game," Posey said. "He's pitching with a lot of conviction, and I think one of the reasons he's doing that is he's so well-prepared."
Zito concurred. "For me, it's about preparation," he said. "Knowing the opponent, studying them, knowing their tendencies, knowing their sweet spots and their weak spots."
Offense remained a weak spot for the Giants, who own a team batting average of .221. They seized upon a St. Louis defensive lapse to score the game's lone run in the fourth inning, one inning after they left the bases loaded.
With one out, Gregor Blanco walked and Brandon Crawford singled, requiring a sacrifice-bunt attempt from Zito. He indeed tapped a bunt almost halfway toward the pitcher's mound. That prompted Molina, the catcher who has won five consecutive Gold Glove Awards for fielding excellence, to wave off Westbrook to make the play. But Molina dropped the ball, enabling Zito to reach first and load the bases.
"I missed it. Pretty simple, I missed it," Molina said. "I took my eyes off the ball and missed it."
Angel Pagan coaxed a four-pitch walk from St. Louis starter Jake Westbrook, scoring Blanco.
San Francisco won its fifth consecutive home opener and improved to 11-3 in that category since christening AT&T Park in 2000.