Showers delayed the game twice, first and most dramatically for 47 minutes in the bottom of the fifth inning immediately after Taveras homered. The thunderstorm echoed the thunderclap of Taveras' drive, which he delivered in the second at-bat of his Major League debut.
Freshly recalled from Triple-A Memphis, Taveras jumped on Petit's 1-0 curveball.
"Everybody knows it's gone," said Taveras, 21. "That's what was going through my head."
"He has a good swing," Petit said of Taveras. "He swings hard. He pulls everything. That's why I wanted to stay [outside]."
Instead, Petit's breaking pitch strayed toward the middle of the strike zone.
"That was the one mistake I made today," said Petit (3-3), who yielded only one other hit in six innings, Matt Carpenter's fourth-inning single.
Busch Stadium fans, starved for offense from the inconsistent Cardinals, deliriously cheered Taveras and got the young phenom to make the curtain call they demanded.
"He took advantage, and he hit it well," Giants manager Bruce Bochy said of Taveras. "I'm sure that's what they're looking for, a guy who's going to provide some power."
Petit still provided encouragement as the Giants absorbed their second defeat in 10 games. Replacing Matt Cain, who officially went on the disabled list with a strained right hamstring, Petit improved vastly upon his previous three substitute starts, during which he allowed 16 earned runs in 14 1/3 innings.
"I was proud of our guy," Bochy said. "He gave us a chance to win. That's all you can ask."
Having amassed 15 runs and 20 hits while defeating the Cardinals in the series' first two games, the Giants mustered their only three hits in six innings off Wacha, who was accustomed to such soggy surroundings. According to the Cardinals, Wacha has made six starts this year that were affected by rain before or during the game. The accompanying delays have totaled six hours and 30 minutes.
With a 2.45 ERA, Wacha's capable of thriving in any conditions. He repelled two minor threats, surviving Michael Morse's leadoff double in the second inning, then weathering two-out singles by Hunter Pence and Pablo Sandoval in the sixth inning. Sandoval's line drive lengthened his hitting streak to 11 games.
Downpours stopped play again for 51 minutes in the top of the seventh inning. The second delay didn't disrupt the Cardinals pitchers, though it forced Wacha to shut down. By then, it was too late. Wacha lasted long enough for the Cardinals to activate their top relievers -- including closer Trevor Rosenthal, who displayed his 98 mph fastball while striking out Pence, Sandoval and Morse in the ninth inning.
The Cardinals added a seventh-inning run off George Kontos, who yielded Allen Craig's leadoff single and Jhonny Peralta's two-out RBI double.