Had Posey been safe, San Francisco would have taken a one-run lead with the opportunity to bring their closer, Santiago Casilla
, in to pitch in the bottom of the ninth.
"What a big play, big call," said Giants manager Bruce Bochy, who almost immediately challenged the ruling on the field.
San Francisco eventually won, 2-1, but the replay decision also helped set the stage for one of the most memorable postseason games ever, lasting a playoff-record six hours and 23 minutes and tying the mark for innings with 18.
Here was the setup: The Giants, who had been shut down all night, finally put together a two-out rally. Joe Panik walked. Posey singled to put runners on first and second, bringing Sandoval to the plate.
Sandoval sliced a line drive into the left-field corner. Panik scored easily. Third-base coach Tim Flannery, seeing that Posey reached third just as left fielder Bryce Harper was picking up the ball, waved the runner home. Harper quickly got the ball to shortstop Ian Desmond, who made a strong relay throw to the plate.
Flannery made his decision based on several factors, including how long it took Harper to get to the ball, the situation, the fact that the Nationals would have to execute almost flawlessly to record the out and the knowledge that this was the first real scoring opportunity that San Francisco had managed all night.
"I was trying to win," Flannery explained. "There were two outs. The ball was down in the corner, and it took him a while to dig it out. It took two perfect throws. And we play to win."
The ball got to the plate well before Posey, but catcher Wilson Ramos couldn't immediately apply the tag. And the runner was ...
Out, said Carapazza.
Not so fast, countered Bochy, who had everything to gain and little to lose by challenging.
While the replay officials in New York studied the play, several angles were shown both to the viewing audience and on the giant video screen at Nationals Park. Sure enough, one appeared to show that Posey's foot was above the plate when he was tagged.
The official announcement was that the call stands, meaning there wasn't enough evidence to overturn it.
Posey admitted he was "pretty gassed" by the time he circled the bases, but he emphatically called himself safe after sliding across the plate. Later, he admitted that he wasn't sure.
"It's one of those where I think if I was called safe on the field, it probably stands," the catcher said. "It was one of those inconclusive ones, I feel, from the replay I saw. But he happened to call me out on the field.
"You could see from the replay how close it was. My foot actually stuck in front of the plate. I think if my foot hadn't caught, I might have been able to get the plate before him, but I didn't."
Bochy also had mixed emotions about decision.
"I don't know how they came up with their call," the manager said. "We saw the replay. It looked like he was safe."
He then added: "I haven't had a chance to look at it."