CINCINNATI -- Jeremy Affeldt and Buster Posey scampered through the Giants' clubhouse, emptying bottles of Mumm Napa Brut Prestige upon each other. Guillermo Mota dumped a container of ice water upon Angel Pagan's head. General manager Brian Sabean conducted a radio interview wearing a T-shirt, having shucked the nicer clothes he wore earlier to avoid having them drenched in the celebration.

And the Giants definitely had reason to celebrate.

Thriving in crucial confrontations and at critical moments made the Giants 6-4 winners in Thursday's decisive Game 5 of the National League Division Series and completed a singular reversal. Posey's fifth-inning grand slam and another scintillating bullpen effort prompted San Francisco's triumph.

After losing the series' first two games, San Francisco won the next three to reach the NL Championship Series, which will begin Sunday against the winner of the St. Louis-Washington NLDS.

"We have plenty of work still," right-hander Sergio Romo said.

This scene unfolded four times in 2010 as the Giants marched to the World Series. But Posey pointed out that this Giants squad includes a mostly new cast of position players.

"It's a new feeling. You can't really compare 2010 and this team," said Posey, whose slam culminated a six-run outburst. "In 2010 we were never down in a series. So it was a different feeling for me to go out and know that it was time to get something done or we were going home."

The Giants made all kinds of history by sending Cincinnati home. Previously, all 21 teams winning the first two games in an NLDS since it was added to the postseason format in 1995 proceeded to capture the series. The Giants became the first club to buck this trend and the only NL team to finish its surge with three consecutive road victories. San Francisco and Cincinnati joined Texas and Tampa Bay in 2010 by playing the only Division Series in which road teams won each game. The Giants also were the eighth team in either league to erase a 2-0 deficit and win a best-of-five postseason series.

From a statistical perspective, the Giants' conquest was wholly improbable. Cincinnati outscored the Giants 22-18, outhit them .261-.194 and recorded a 3.13 ERA, compared with San Francisco's 4.11.

But, as corny as it may sound, numbers couldn't measure the Giants' heart.

They took the field each day emboldened by Hunter Pence's motivational addresses.

"Big kudos to Hunter. That guy got us going," Romo said.

They stopped the Reds when it counted most, limiting them to three hits in 24 at-bats with runners in scoring position over the series' final three games. Two relievers particularly excelled Thursday. Affeldt stranded two runners in the seventh inning by coaxing a comebacker from Ryan Ludwick, who hit a series-high three homers. Romo surrendered a ninth-inning run but recorded the final four outs, including Jay Bruce's fly to left field that ended a 12-pitch standoff.

San Francisco's bullpen had to succeed, because no starter pitched beyond the sixth inning.

"Affeldt, Romo, [George] Kontos, all of them did a great job the whole series," manager Bruce Bochy said.

The most powerful contribution on this sunny yet chilly afternoon at Great American Ball Park came from Posey -- fittingly enough, since he's completing his own comeback. Posey's the favorite to win the NL Most Valuable Player Award one year after sustaining multiple left leg injuries that sidelined him for much of the season.

Thursday initially belonged to San Francisco's Matt Cain and Cincinnati's Mat Latos, the starting pitchers who combined to create a scoreless tie through four innings.

Then Gregor Blanco singled to open the fifth, marking the first time a Giants leadoff batter reached base. Brandon Crawford, who was hitless in eight Division Series at-bats, tripled into the right-field corner on a 2-0 pitch, scoring Blanco. Crawford held as Cain hit a comebacker. Pagan then tapped a grounder to shortstop Zack Cozart, who was drawn in along with the other infielders for a possible play at the plate on Crawford. But Cozart dropped the ball as he cocked his arm to throw home, enabling Crawford to score and Pagan to reach first.

Marco Scutaro walked and Pablo Sandoval singled to load the bases. Up came Posey, who owned averages of .176 (3-for-17) in the series and .250 (7-for-28) with the bases loaded in his career during the regular season. He drilled a 2-2 pitch into the left-field upper deck, an estimated 424 feet from home plate, to launch a spirited round of high-fives, backslapping and other expressions of euphoria in the Giants' dugout.

"I didn't do much the whole series," said Posey, who also homered off Latos in Game 1. "I probably was a little overanxious at times. I was happy to be in that situation."

And the Giants were thrilled to see him there.

"I was getting ready to tag up, believe it or not," Pagan said. "I knew he hit it well enough, but I was just waiting to do my part. When I saw it go into the stands, I had so much joy. It was awesome."

Said left-hander Barry Zito, "Posey has been our guy all year. He's put us on his back."

"It's one of those things where we were just waiting for him to do it," first baseman Brandon Belt said. "We knew it was going to happen sometime. As soon as he got a hold of it, everybody knew. We were ecstatic. It was an awesome feeling."

The Reds weren't finished. They gradually narrowed the deficit with Brandon Phillips' two-run double in the fifth inning and Ludwick's leadoff homer in the sixth. The Giants extricated themselves from further trouble as Posey threw out Bruce on an attempted steal of third base, following Ryan Hanigan's strikeout, to complete a sixth-inning double play.

After Affeldt ended the seventh-inning threat by retiring Ludwick, who represented the potential tying run, the Giants turned to defense in the eighth. With a runner on first and one out, Crawford flung himself to his right to grab Hanigan's line drive. With Reds on first and second and two outs, Pagan dove to snare pinch-hitter Dioner Navarro's sinking liner. That prevented a hit and, quite possibly, a run or two.

"I was going to block it with my teeth to keep it in front of me," Pagan said.

As the ninth began, Romo reflected briefly on his teammates and the coaching staff.

"I'm very proud that they asked me to get the last out," he said. "It means a lot to me that they count on me."

However, Romo walked Cozart with one out before Joey Votto singled. Ludwick also singled, scoring Cozart. Up came Bruce, a two-time All-Star who amassed 34 homers and 99 RBIs this year. Bruce fouled off six two-strike pitches before lifting a full-count slider to left field. From his perspective behind the plate, Posey marveled.

"It's one of the best battles I've ever been a part of," he said.

Up came Scott Rolen, who struck out on five pitches. The Giants' series-long rally was over.

"We believed we could win this series from the get-go," Romo said. "Yeah, we were down, but we were never really out of it. We never hung our heads. We knew that if we stuck together, we could win this. We battled all year long -- ups and downs, injuries, the ball not bouncing our way at times. This is just a culmination of everything up to this point."