As Scutaro squirmed in the infield, twisting in pain, fans at AT&T Park showered Holliday with boos. Giants players watched and worried, fearing the worst for a fallen teammate. Manager Bruce Bochy and trainer Dave Groeschner ran out of the dugout to attend to Scutaro, who finally dusted off the dirt and stood up strongly.

And just like that, so did San Francisco’s offense.

Scutaro singled in two runs during a four-run fourth inning before leaving with a hip injury, sparking San Francisco’s first home win this postseason, 7-1 over the St. Louis Cardinals on Monday night to tie the NL championship series at one game apiece.

“We felt for him,” center fielder Angel Pagan said. “We felt a little bit of anger.”

All those feelings came crashing down on the Cardinals in a hurry.

Scutaro left after the fifth because of a left hip he injured on a play Giants manager Bruce Bochy felt was illegal. X-rays were negative, and Scutaro likely will get an MRI exam on Tuesday. There was no word on his status, but closer Sergio Romo said when Scutaro left, the second baseman “had a little smile on his face that he’d be back. Definitely not really worried right now.”

“In my opinion,” right fielder Hunter Pence said, “it pumped us up a little bit.”

The series now shifts to St. Louis for three games, starting Wednesday when San Francisco ace Matt Cain takes on Kyle Lohse of the Cardinals, and the Giants are already rallying behind the slide against Scutaro.

Things got testy when Holliday barreled into Scutaro at second base to break up the potential double play in the first inning. The play riled up fans that had seen three straight losses by the Giants so far this postseason and still hold fresh — and sensitive — memories of the home-plate collision that sidelined All-Star catcher Buster Posey most of last season.

“In hindsight, I wish I would have started the slide a little earlier, but it happened so fast,” Holliday said. “I hope he’s OK, he’s a good guy. I was more interested in breaking up the double play.”

There was plenty to cheer all night for Giants supporters.

Ryan Vogelsong pitched seven strong innings, Pagan hit a leadoff homer to give San Francisco its first home lead this postseason and Scutaro stayed in until breaking the game open with his single off Chris Carpenter.

“That shows you how tough he is,” Bochy said. “I really think they got away with an illegal slide there. That rule was changed a while back. And he really didn’t hit dirt until he was past the bag. Marco was behind the bag and got smoked. It’s a shame somebody got hurt because of this. That’s more of a roadblock.”

Making Scutaro’s hit even sweeter for the Giants was the fact that Holliday misplayed the ball in left field, allowing a third run to score on the error and Scutaro to advance to second.

“There’s baseball gods. There’s definitely baseball gods,” said former Giants first baseman and current special assistant Will Clark, whose takeout slide in July 2008 of St. Louis second baseman Jose Oquendo, now the Cardinals third base coach, set off a brawl. “There’s a reason why he hits a (single) and Holliday boots the ball he hit. Baseball gods shine in weird ways.”

The Giants also benefited from a missed call by an umpire in the eighth inning after St. Louis center fielder Jon Jay made a spectacular, diving catch to rob Brandon Crawford of a hit.

Jay threw toward first and the Cardinals should have gotten a double play, but first base umpire Bill Miller did not see Allen Craig tag Gregor Blanco’s jersey as he raced back to first on the play.

St. Louis manager Mike Matheny argued the call and the umpires huddled to discuss it, but they kept the safe call even though replays showed Craig made the tag. The Giants capitalized when Ryan Theriot hit a two-run single to make it 7-1.

“I’m not going to take a hard stance one way or another on the replay,” Matheny said.

“That really wasn’t the game today,” he said. “But every once in a while there’s a big play that does change the course of the game and I’m not against having something else to help get it right.”

Back at Busch Stadium, Holliday will be cheered after being the target of boos all night following his aggressive play on the basepaths.

With runners on first and second and one out in the first, Craig hit a bouncer to Crawford, and the shortstop quickly flipped to Scutaro for the forceout. Holliday, a former high school football star in Oklahoma, came tumbling in and slid late into Scutaro, buckling his left leg to prevent the double play.

“A lot of guys take pride in breaking up double plays. Holliday is one of them,” Cardinals second baseman Daniel Descalso said. “On slowly hit balls you’re going to get hit. You don’t want anyone to get hurt, but I’m all for playing the game hard.”

Vogelsong got out of the jam by retiring Yadier Molina on a groundout to short.

“I just really was trying to make the next pitch to get the guy out so we could get him in the dugout,” Vogelsong said.

Scutaro stayed in the game with a limp until being replaced in the sixth by Theriot. By then, he had done his damage with the bat in the big fourth inning.

The rally started innocently enough with a bloop, opposite field double by Brandon Belt and a chopper over third baseman David Freese by Blanco. Crawford then hit a bouncer between the mound and first base that Carpenter fielded and threw short and left of first base, allowing Belt to score. It appeared Crawford may have impeded Carpenter by running slightly inside the baseline, but the Cardinals did not argue the play.

After Vogelsong’s sacrifice bunt advanced the runners to second and third, Pagan walked to load the bases with two outs and Scutaro lined his single to left-center that Holliday misplayed to the delight of Giants fans, putting Carpenter and the Cardinals into a 5-1 hole.

“He’s a clutch hitter, he always has been, I know that since he’s been over here,” Carpenter said. “He’s not going to miss those opportunities.”

Vogelsong made the lead hold up by becoming the first Giants starter to make it through six innings this postseason. He allowed four hits and one run for his first career postseason win.

These teams have a history of contentious meetings in the NLCS, from Jeffrey Leonard’s one-flap down home run trot in 1987 that riled up the Cardinals to a benches-clearing dustup 10 years ago when St. Louis reliever Mike Crudale buzzed Kenny Lofton after he showboated on a home run.

San Francisco answered with the bats this time as Pagan led off the bottom of the first with a homer — matching his feat from Game 4 of the division series against Cincinnati. The Giants had been outscored 20-6 and never led in two home losses to the Reds and the Game 1 defeat to the Cardinals.

Pagan’s shot came soon after Scutaro was wiped out.

“I haven’t seen the replay, so I can’t judge if it was dirty or not,” Pagan said. “Any time you see a teammate fall down like that, you really feel for him.”

The Cardinals tied it in the second inning when Pete Kozma drew a two-out walk and scored on Carpenter’s RBI double, his third hit already this postseason.

But Carpenter, making his fifth appearance in 2012 after complicated surgery to remove a rib and two neck muscles, wasn’t nearly as sharp on the mound or in the field. He allowed five runs — two earned — and six hits in four innings, failing to add to his 10 career postseason wins.

NOTES: Philadelphia’s Jimmy Rollins is the only other player with two leadoff homers in a single postseason, doing it in 2008. … Cardinals OF Carlos Beltran reached base three times, doubling twice and walking once. … Giants 3B coach Tim Flannery performed the national anthem with the Grateful Dead’s Bob Weir and Phil Lesh.

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