San Francisco Giants relief pitcher Sergio Romo, center, celebrates with teammate after the Giants defeated the Cincinnati Reds 6-4 in Game 5 of the National League division baseball series, Thursday, Oct. 11, 2012, in Cincinnati. The Giants won the final three games, all in Cincinnati, and advanced to the NL championship series. (AP Photo/Michael Keating)
CINCINNATI -- Buster Posey insisted all along -- even after San Francisco lost the first two at home -- that his team was far from done, no matter how long the odds.
Turns out, he was right. And the NL batting champion had a lot to do with this most Giant comeback.
Posey hit the third grand slam in Giants postseason history on Thursday, and San Francisco pulled off an unprecedented revival, moving into the championship series with a 6-4 victory over the Cincinnati Reds.
They'll play either Washington or St. Louis for the NL pennant starting Sunday.
"We could go up against anybody at any time," shortstop Brandon Crawford said. "Being down 2-0 and coming back and winning three at their place, it's an unbelievable feeling."
The Giants became only the eighth team to win a five-game playoff series after falling behind 2-0. Major League Baseball's changed playoff format this season allowed them to become the first to take a best-of-five by winning the last three on the road.
With one swing, Posey made it possible.
"I don't think anybody gave up," he said.
Posey's second career grand slam off Mat Latos put the Giants up 6-0 in the fifth and sparked a joyous scrum in the San Francisco dugout. The ball smacked off the front of the upper deck in left field, just above Latos' name on the video board.
"That gave us some breathing room," reliever Jeremy Affeldt said. "We were all excited."
Will Clark, in the 1989 NLCS, and Chuck Hiller, in the 1962 World Series, hit the other Giants slams in the postseason.
Matt Cain and the bullpen held on, with more help from Posey. The All-Star catcher threw out Jay Bruce at third base to snuff out a sixth-inning rally that cut it to 6-3. The Giants also had a pair of diving catches that preserved the lead in the eighth.
Ryan Ludwick singled home a run in the ninth off Sergio Romo. With two runners aboard, Romo fanned Scott Rolen to end it. The Giants raised their arms, hugged and huddled by the side of the mound, bouncing in unison.
Then they were off to the visiting clubhouse to start spraying some bubbly.
In Cincinnati, the home-field meltdown felt sickeningly familiar. The Reds haven't won a home playoff game in 17 years. After taking the first two on the West Coast, all they needed was one more at home, where they hadn't dropped three straight all season.
"You get tired of the disappointments, but then you get over it," manager Dusty Baker said. "It hurts big-time."