CINCINNATI – A third straight road victory over the Cincinnati Reds that transformed the Giants' season from improbable to historic also left closer Sergio Romo drenched, exhausted and emotional.

As his teammates celebrated a 6-4 series-clinching win, Romo stood in a corner of the clubhouse, hands on bent knees, eyes welled with tears. He had given every ounce of himself with a 35-pitch save, and the magnitude of the moment hit him.

The Giants had just become the first team in major league history to wipe out a two-game deficit in a best-of-five series by winning three straight on the road, and Romo had sealed the deal. He got four outs, including a flyout to end an epic 12-pitch battle with Jay Bruce, who represented the winning run in the ninth inning.

"I'm just very proud to be the guy they asked to get that last out," Romo said quietly. "I couldn't let them down. It's easy to be emotional about things like this because it's good emotion."

The Giants have been riding positive emotions since they stepped into the Reds' home park. It started with Hunter Pence's speech Tuesday, which became a pregame ritual when the Giants won in extra innings that night to stave off elimination.

The message always is a simple one: "Let's give ourselves another day together, another game together."

Behind Romo's heroics, Matt Cain's resilience and Buster Posey's monster grand slam, the Giants clinched at least four more games together. They advanced to the National League Championship Series for the second time in three years and will face either the St. Louis Cardinals or Washington Nationals.

Posey provided the decisive blast, a fifth-inning grand slam off of Mat Latos to give the longtime Giants foe another reason to continue signing baseballs with the phrase "I hate SF!"

San Francisco couldn't possibly have more love for Posey, who displayed a rare bit of bravado after crushing a 2-2 fastball from Latos. He watched the ball soar an estimated 434 feet into the left-field stands as Latos and Reds catcher Ryan Hanigan walked in the other direction, suddenly trailing 6-0.

"This is probably right behind the World Series win," a smiling Posey said of the three-game comeback tour.

The Giants have always struggled against Latos, who had a 2.19 ERA in 11 career starts against them and pitched four strong relief innings in Game 1. But Gregor Blanco drew first blood in the fifth inning, lining a single and scoring on Brandon Crawford's triple, his first career postseason hit.

Crawford scored on an error and the Giants loaded the bases ahead of Posey, who at 25 already has a résumé that includes a World Series title, Rookie of the Year award, and possibly soon, a selection as MVP.

He added to the list Thursday. Posey joined Chuck Hiller (1962) and Will Clark (1989) as the only players in franchise history to hit a postseason grand slam. Yogi Berra (1956) and Eddie Perez (1998) were the only two previous catchers in major league history to have hit one in the playoffs.

"I was happy to come up in that situation," Posey said. "Those are the types of spots you work really hard for and try to enjoy."

Even with a six-run lead, the Giants weren't able to enjoy the next three innings. The Reds kept pushing, but each time they were knocked back by a stellar defensive play by the Giants. Posey capped a huge sixth-inning strikeout of Hanigan by throwing Bruce out as he attempted to steal third.

Bochy said he had just one tough lineup decision to make before the winner-take-all game, and he stuck with his gut and Crawford, one of the best defensive shortstops in the game. Crawford rewarded that faith not only with the triple, but also with a diving catch to rob Hanigan with a runner on in the eighth.

The Reds brought the tying run to the plate in the final four innings, and when they threatened in the eighth, Bochy called for Romo. His first opponent, Dioner Navarro, hit a sinking liner to center, but Pagan made a spectacular sliding catch to end the inning.

"You can't let that ball get past you," Pagan said. "I was going to block that with my teeth if I had to."

Romo used different parts of his body when he came on for the tense ninth.

"You saw guts," Pence said. "He's all heart," Pagan added.

Romo walked one and gave up two singles as the Reds inched closer in the ninth. Bruce wouldn't give in with two runners on, fouling off nine pitches.

"He had the same attitude as me: 'This guy is not going to beat me,' " Romo said.

Romo won the showdown.

Bruce flied out to left, and a strikeout of Scott Rolen sealed the win for the Giants, the eighth team in history to come back from a two-game deficit in a five-game series.

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