The culprit was pitcher Clay Hensley, who, as corroborated by several teammates, prophesied Posey's no-doubter. As Pagan galloped to the dugout seconds after touching home plate, Hensley, part of a raucous dugout celebration, couldn't contain himself, and accidentally applied a jab to the side of Pagan's smiling face.
"We were just going nuts," said southpaw Barry Zito. "We didn't know what was happening. I think he gave Pagan a right uppercut."
That Posey's 434-foot swat sent his teammates into a frenzy encapsulates the Giants' season. The catcher entered the contest with just three hits in 15 at-bats in the series. When he flexed his muscles at a critical juncture, however, the result was the most damaging swing the game of baseball permits. The grand slam -- the first surrendered by Reds starter Mat Latos in his career and the third in a winner-take-all playoff game in Major League history -- lifted the Giants to a six-run lead, too big a deficit for the Reds to overcome.
"I don't really like saying that there are moments in games where you shift momentum," said Reds first baseman Joey Votto, "but when Buster hit that grand slam -- six runs is so difficult to come back from. That we almost came back was pretty impressive. But Buster totally broke our back with that swing."
Ballots for regular-season awards were submitted prior to the start of the postseason, so Posey's clutch club won't influence his position in the battle for the NL's Most Valuable Player. Still, if a memorable season requires a defining moment, Posey delivered his on this chilly afternoon beside the Ohio River.
"Posey has been our guy all year," Zito said. "He's put us on his back."
Posey appeared in only 45 games last year, most of his season taken out from under him -- in both a literal and physical sense -- when a collision at home plate resulted in a broken leg and torn ligaments in his ankle. Missing their heart and soul, the Giants also missed the postseason.
This time around the Giants surged into the playoffs after capturing the NL West. After Cabrera drew a 50-game ban, the team embarked on a 30-15 stretch to close out the regular season. Posey finished with a league-best .336 batting average to go along with 39 doubles, 24 homers and 103 RBIs.
So when the opportunity arose for someone to submit a season-shifting knockout punch, who better to provide it than Posey?
"He's a leader on this club," said skipper Bruce Bochy. "He leads by example."
Posey's teammates certainly weren't surprised by the rocket to left field, but that didn't stop them from inciting a celebration that was only a precursor of the one they carried out in the clubhouse a little while later.
"It's one of those things where we were just waiting for him to do it," said first baseman Brandon Belt. "We knew it was going to happen sometime. As soon as he got hold of it, everybody knew. We were ecstatic.
"It was an awesome feeling."