Yadier Molina helped relieve some of the pressure on Garcia by hitting a three-run home run to cap a four-run second, and the young pitcher never looked back.
"He's a rookie, but he acted like a veteran," Molina said. "He's a rookie, but he doesn't show any emotion out there. Was he nervous? It doesn't show, but I'm pretty sure he was."
The Brewers are known to be tough against left-handed pitchers, and Ryan Braun, who has a career batting average of .362 against southpaws, was batting in his usual third spot Saturday.
That didn't deter Garcia. He held Braun hitless in three at-bats, with two groundouts and one deep ball that right-fielder Ryan Ludwick caught on the warning track.
"They're one of the better teams against left-handed pitching, and he was outstanding against them," Cardinals manager Tony La Russa said. "He made a lot of good pitches. You just can't give him enough credit, especially against a club like that."
Garcia (1-0) was making his second Major League start. He had elbow surgery in September 2008 and spent last year rehabbing and pitching for Triple-A Memphis.
He also was facing Milwaukee's ace, Yovani Gallardo (0-2), who was making his first start since signing a five-year, $30.1 million contract earlier in the week.
"Their pitcher is a great pitcher," said Garcia, who had his parents in the crowd at Miller Park and was given a beer shower by teammates in the runway to the locker room after the game.
"We were able to score some runs against him early in the game, and I was able to keep our team in the game," Garcia said.
Garcia calmly sent the Brewers down in order during three of his six innings, including the first two. He had a 4-0 lead after two innings thanks to Molina's home run, and got Carlos Gomez out in two critical spots. He struck out Gomez with two runners on to end a threat in the third, and got him to bounce into a bases-loaded fielder's choice to end the fifth.
"He threw a lot of balls that were running away from us [right-handed hitters]," Milwaukee's Corey Hart said. "With a lefty, you usually don't see that. And he threw a lot of fastballs that were tough to square up."
The early home run by Molina gave Garcia some breathing room.
"It helped everybody get comfortable, but any time you have a team like Milwaukee, you can't get too comfortable," Molina said. "They've got a very good lineup. He kept pounding that sinker down and got quick outs."
Gallardo didn't pitch poorly, but Molina was looking for a pitch high in the strike zone, and he got a fastball right where he was looking.
"That's not my game," Molina said of hitting homers. "I don't think that way. I just try to put on a good swing and whatever happens, happens. I just do my best to try to help the team to win, whatever it is."
Although he's not known for home runs, La Russa said Molina is known as an RBI threat.
"He already has a reputation among people in uniform," La Russa said. "I hear that all the time. Coaches and managers and players, they fear Yadi like they do Albert [Pujols] or [Matt] Holliday or anybody."
Pujols had a two-run single in the fifth that made it 6-0. Colby Rasmus also homered, hitting the first pitch of the sixth into the right-field bleachers for his second homer of the year.
"To score runs is good for the team, but I have to keep the same mentality," Garcia said of pitching with the lead. "It worked out really good."