SAN FRANCISCO -- The showers that drenched AT&T Park toward the end of Monday night's game seemed surreal.

"We haven't had rain like that in a long time," Matt Cain said.

But the precipitation provided a nice segue to the waterworks in the Giants clubhouse, where ballplayers sprayed each other with champagne to celebrate their latest triumph.

And what a triumph it was. Completing their second rare comeback of the postseason, the Giants subdued the St. Louis Cardinals, 9-0, to win Game 7 of the National League Championship Series and advance to a World Series confrontation against the Detroit Tigers.

San Francisco's five-run surge in the third inning, launched by the second of three hits from series Most Valuable Player Marco Scutaro, backed Cain, who worked 5 2/3 innings before turning the game over to the bullpen. Cain sustained the excellence of the Giants' starters, who yielded one run in 20 1/3 innings during the series' final three games.

The Giants sealed their fifth pennant since moving to San Francisco in 1958 by winning six consecutive elimination games, matching a standard set by the 1985 Kansas City Royals. The Giants overcame a 3-1 deficit in the best-of-seven NLCS by fending off St. Louis three games in a row, which followed three consecutive victories that erased a 2-0 disadvantage in the best-of-five Division Series against Cincinnati.

"Incredible," Giants manager Bruce Bochy said. "I'm still numb."

Bochy led a group of resolute professionals who refused to quit. The Giants became the 12th team out of 77 that trailed 3-1 in a best-of-seven series yet emerged triumphant. They're also just the fifth NL club to achieve this distinction.

"We've made a lot of good memories so far," catcher Buster Posey said. Turning his attention briefly to the World Series, which begins here Wednesday, Posey added, "We still have a lot of work to do."

First, the Giants wanted to revel in their comeback against the Cardinals, who happened to be the reigning World Series champions. San Francisco outscored them 20-1 in the final three games in a dramatic reversal.

"They played better baseball than us. Bottom line," St. Louis right fielder Carlos Beltran said.

Referring to the last three games, Beltran added, "We made a lot of mistakes and they didn't make any mistakes. They were able to put things together -- offense, defense and pitching -- and we couldn't do that. I think that was the difference."

The turnaround began with the Giants' Game 5 victory behind Barry Zito, which brought the series back to San Francisco.

"He was a momentum-shifter for us," Cain said. "We felt like we had a lot going for us, especially getting back in front of these fans."

Hosting the first Game 7 played in San Francisco since the 1962 World Series, the Giants jumped ahead by scoring in each of the first three innings off Cardinals starter Kyle Lohse. The right-hander allowed seven hits while walking five in Game 3 yet somehow yielded just one run in 5 2/3 innings. Lohse's luck ran out this time before a roaring AT&T Park crowd that showed up eager for the Giants' first series-ending Game 7 victory in franchise history.

"The energy that the stadium had today was awesome," Cain said. "I think we really fed off that."

Cain helped the Giants apply the early pressure upon the Cardinals with a second-inning RBI single. It marked the first time that pitchers have driven in runs in three consecutive postseason games, as Cain extended the streak started by Zito and Ryan Vogelsong.

Leading 2-0, San Francisco loaded the bases in the third on Scutaro's single, Pablo Sandoval's double and Posey's walk, which finished Lohse. Hunter Pence, batting .159 (7-for-44) in the postseason, lined reliever Joe Kelly's first pitch on a hop past shortstop. The ball spun oddly in the grass -- probably because Pence's bat shattered yet made contact with the pitch perhaps three times, as television replays indicated. Center fielder Jon Jay swooped over to scoop up the ball but missed it. The error enabled Posey, beckoned frantically by third-base coach Tim Flannery, to follow Scutaro and Sandoval home.

"You never know what's going to happen next," Giants right-hander Sergio Romo said. "It was a big hit for us, regardless of how many times he hit it."

Brandon Belt chopped a grounder that Kelly unsuccessfully tried to barehand, resulting in a single. Blanco walked to load the bases again, setting up run-scoring, fielder's-choice grounders by Brandon Crawford and Angel Pagan.

That provided ample support for Cain, who staggered on a tightrope during the first three innings but remained upright. After stranding Beltran on second base in the first inning, Cain was rescued one inning later by Crawford, who timed his leap perfectly to snare Lohse's soft liner toward shortstop and leave runners on second and third.

"It was tough because it was straight over my head," Crawford said. "So I couldn't turn right or turn left and then jump. I had to go straight up. That made it harder. But with Cain pitching the way he did, I knew I had to make a play."

Jay singled to open the third inning but was left on third base when cleanup hitter Allen Craig flied out.

"I think those first two or three innings were probably the turning points of the game," Posey said. "Because if they get on the board quick and get a little momentum, it could be a different game. I think Matt did a great job of shutting them down."

The cumulative effect was overwhelming. Nothing, it seemed, could stop the Giants, who added two late runs, the last coming on Belt's eighth-inning homer.

"Tonight just seemed to be our night," Pence said. "We got all the breaks. You could have played this game 100 times and it could have gone 50-50. The breaks were on our side."