San Francisco Giants lefthander Madison Bumgarner was the beneficiary of some unexpected largess from his teammates Monday at Busch Stadium.

In his six previous starts, the 21-year-old Bumgarner had given up just nine earned runs, but the Giants also had scored only nine runs while he was on the mound. Ergo, he entered his start against the Cardinals as probably the best 1-6 pitcher in the baseball.

Thanks to a key fourth-inning walk he cadged from Cardinals starter Kyle McClellan, loading the bases for Andres Torres' decisive grand slam two pitches later, Bumgarner moved to 2-6 for the season. And the Giants scored as many as seven runs for only the third time this month in a 7-3 thumping of the Cardinals.

A North Carolina native, Bumgarner enjoyed the rare opportunity to pitch in 90-degree heat. "This feels like home. I knew what to expect," he said.

Bumgarner held the Cardinals to two runs in seven innings, both runs scoring in the third, with the help of a call the Giants mildly disputed on a double over third base by Allen Craig.

"For a young kid, he's got great poise," said manager Bruce Bochy. "He knew this was an important win for us after a couple of tough ones in Milwaukee."

After scoring a total of just one run in their last two games in Milwaukee over the weekend, the Giants had lost three of their first four games after the crunching left leg injury suffered by star catcher Buster Posey, who is out for the balance of the season.

The Giants' second win since the home-plate collision Posey endured Wednesday night in San Francisco came much the way their first win did. After rookie shortstop Brandon Crawford hit a grand slam for his first big-league hit to win a game Friday in Milwaukee, Torres on Monday hit his first grand slam, he surmised, since 2004 or 2005 in the Puerto Rican winter league.

McClellan trailed only 3-2 and had Bumgarner down in the count at 1-2 in the fourth with runners at second and third and one out. But Bumgarner walked.

"Certainly, Bumgarner drawing the walk was huge," said Bochy. "McClellan has been throwing the ball very well. He was a little off today. That's all that is. But give Bumgarner credit for drawing that walk.

"(The pitches) weren't really that close where 'Bum' could swing at them. He probably would have, to be honest. I'm sure there's frustration on (McClellan's) part."

The inning before, Bumgarner had doubled and scored the Giants' second run, so he did not appear overmatched with bat in hand. But he was almost overrun on the bases by Torres, whose homer was just his second of the season.

"(The power) has been missing. You can certainly see that by the numbers," said Bochy, whose team was 14th in home runs in the National League with 35 homers in 52 games before Monday.

Posey, the National League's rookie of the year for 2010, went out with a .284 average and 21 runs batted in, and Bochy admitted the aftershock of Posey's injury took a toll.

"The next day there was a hangover," said Bochy. "The guys took it hard.

"But at the same time, you shake yourselves out of this. That's what Buster would want, to hold the fort down."

The Giants won't get Posey back this year. But they are awaiting the return in the next 10 days or so of third baseman Pedro Sandoval, still tied for the team lead in home runs at five despite not playing at all this month because of a fractured bone in his right wrist suffered in late April.

"That," said Bochy, "will make a big difference. He's really been our best hitter."