Angel Pagan's fourth-inning, bases-loaded walk was the lone score, and Barry Zito tossed seven scoreless innings, as the defending World Series champion San Francisco Giants topped St. Louis, 1-0, in the opener of a three-game weekend set.
Zito (1-0) surrendered only three hits and walked three while fanning four for the Giants, who raised their second championship banner in three seasons in front of a sellout crowd on Friday.
Sergio Romo tossed a perfect ninth for his third save.
Jake Westbrook (0-1) was the hard-luck loser, charged with an unearned run and six walks on six hits in 6 2/3 frames for the Cardinals, who have lost three of four to start the year.
St. Louis has scored one run over its last three games in the Bay Area, dating back to Games 6 and 7 of last year's NLCS, won by the Giants after they trailed three games to one.
"It was great for us to come out and obviously match up with the Cardinals again," Zito said. "They're a difficult team."
San Francisco threatened in the third, loading the bases on a single from Zito and walks to Pablo Sandoval and Buster Posey, but Westbrook got Hunter Pence on a grounder to end the inning.
Westbrook was burned in the fourth. A one-out walk to Gregor Blanco and a Brandon Crawford single preceded Zito's sacrifice bunt try that Cards catcher Yadier Molina failed to grip. Pagan then worked a base on balls to force in a run.
"I was fighting my delivery a little bit," Westbrook said. "I made a slight adjustment in my delivery and was able to get back into it."
St. Louis put two on with two out in the seventh but failed to produce a run after an inning-ending fly to center from Pete Kozma which capped Zito's performance.
Westbrook finished his outing in the home half with two on and two down, but Randy Choate got Brandon Belt on a line out to end the inning.
Jeremy Affeldt turned aside all three batters he faced in the eighth, and Romo shut the door in the ninth.
Zito hasn't lost a game since Aug. 2, 2012, a 9-1 loss to the Mets, and San Francisco has won 15 in a row when the veteran left-hander takes the mound ... In the season's first four games, Giants starters have failed to give up an earned run over 26 innings ... The clubs split six meetings in the 2012 regular season ... Crawford and Allen Craig were the only players on either squad to collect more than one hit.