SAN FRANCISCO -- Manager Mike Matheny gave the directive to bullpen coach Dyar Miller, who summoned Joe Kelly to join him in a jog to the 'pen.

A once-seemingly safe six-run St. Louis lead had already shrunk to two, and Lance Lynn was giving little indication that he was about to stop a surging San Francisco offense. And so, as Lynn faced pinch-hitter Aubrey Huff -- a batter he'd eventually walk -- Kelly rushed through his warmup sequence.

Kelly had time for about 10 fastballs and another five offspeed offerings before he was jogging again, this time to the AT&T Park mound. Wondering himself if he had had ample time to prepare, Kelly -- with an assist from a diving Daniel Descalso -- closed the inning, setting off a stellar bullpen stand that ensured the Cardinals would exit Sunday with a 6-4 win to open the National League Championship Series.

"As young as they are, I look at their demeanor, and that's the coolest thing about this," said David Freese, speaking specifically of Kelly and fellow rookie reliever Trevor Rosenthal, who also came up clutch in Sunday's game. "They get on that bump with 50,000 people roaring at them, and they don't care."

Indeed, in a game that opened with the Cards racing out to a six-run lead, it took a boost by the bullpen to pluck home-field advantage away from the Giants. The same bullpen that posted a pedestrian 3.90 ERA during the regular season has now allowed only six earned runs in 30 postseason innings.

That's after six relievers combined to toss 5 1/3 shutout innings behind Lynn on Sunday.

"We've got a good bullpen, a strong bullpen, and we have to be ready," Edward Mujica said. "We have to be ready in different situations, no matter what situations. If the starters go four or five, just try to pick them up."

The needed pick-me-up came unexpectedly, as it appeared early that the defending World Series champs were going to cruise. The Cardinals took no time hushing the San Francisco crowd, and they chased left-hander Madison Bumgarner from his start before he could finish four innings.

Freese's two-run homer -- his first postseason long ball since the iconic blast he sent over the center-field wall in the 2011 World Series -- gave St. Louis the early advantage.

"We were ready for mistakes," said Freese, whose six postseason home runs are tied for the third most in franchise history. "Coming in here, we were wanting to get a lead early."

The bottom of the Cards' lineup then sparked a four-run fourth.

Surprising postseason contributors Descalso and Pete Kozma delivered consecutive one-out doubles. Jon Jay extended the inning with a two-out, two-strike RBI single. Carlos Beltran, whose career made a brief stop in San Francisco last season, then drilled a 3-2 slider into the stands.

At the time, Beltran joined Albert Pujols and Babe Ruth as the only players with at least 14 homers and a .325 batting average in the postseason. It was his third home run in seven playoff games this month.

"I'm just really enjoying myself, honestly," Beltran said. "Right now, I'm seeing the ball well. ... I'm not trying to do too much, good things are happening. I feel good about that."

With Lynn having held the Giants hitless through three innings, a six-run cushion seemed plenty substantial. But the club that overcame that same deficit to send Washington to an early winter endured a similar scare from San Francisco. Before the fourth inning ended, the Giants had chased Lynn from the game and climbed back to within two.

They did it with four consecutive two-out hits, including a two-run triple by Gregor Blanco and a subsequent RBI double by Brandon Crawford. It wasn't until after Crawford's knock that the bullpen stirred.

"I threw a lot of fastballs early, and then they started jumping on it and got a lot of big hits in a row," Lynn said. "Before I knew it, they had four runs. I wasn't able to make as quick an adjustment as they did."

When Lynn walked Huff, Matheny made his move.

"His fastball looked good, but when he was working behind in the count, it serves into a team like the Giants' hand," Matheny said. "And they've got an explosive offense and made a strong run and put Lance in a hard spot."

Descalso's diving stop helped Kelly retire Angel Pagan and halt the inning, and a formidable line of arms took their turns from there. Not one of them buckled.

Rosenthal and lefty Marc Rzepczynski bridged the gap to the team's three late-inning arms with scoreless appearances. Mujica, Mitchell Boggs and closer Jason Motte followed in similar fashion.

"Their bullpen's pretty tough," said Pagan. "That's why we have to score some runs against their starters so we won't have to face the nasty guys."

The game ended with the 'pen retiring 14 of the last 16 Giants hitters. That meant that, while down only by two, San Francisco managed to get the potential tying run to the plate only twice after the fifth.

The first came with Rosenthal on the mound in the sixth, and the 22-year-old powered his way past Pagan with six straight 99-mph fastballs. The Giants had one last gasp in the ninth, when Pagan singled with two out. Motte answered with a game-ending groundout.

"It's contagious," Motte said of the bullpen's success. "Just like over the first couple of innings, the hitting was contagious."

The Cardinals needed the nearly perfect bullpen stand, too, because San Francisco's relievers were just as dominant, holding St. Louis hitless after the fourth. The combined 10 2/3 innings of scoreless relief from the two clubs set an LCS record.

It was the Cards, though, who rode the relief to a win, one that puts history on their side. Over the past 20 years, the club that won the first game of the NLCS has advanced to the World Series all but four times.

"People are going to look at the Cardinals and say, 'Well, they only won 88 games and were the second Wild Card,'" said Lance Berkman. "But if we had this team for the entire season, we would have won 100 games easy. If we have a lead after five innings, you're going to be facing five guys that throw 100 mph. That's a tough task for any team to overcome."