PHOENIX -- It's safe to say that as Buster Posey goes, so go the Giants.

National League Rookie of the Year in 2010, the Giants win the World Series. League MVP and batting champ in 2012, and they win it all again.

During the interim years of injury and decreased production, the Giants don't even come close.

"He's set the bar so high," Giants manager Bruch Bochy said.

Posey began raising the bar again Monday night in a 9-8 season-opening win over the D-backs. When the money and all the pressure was once again on the line in the ninth inning, Posey got hold of an Addison Reed fastball and sent it about as far as a ball can go in left-center at Chase Field.

The two-run homer hit the end of the facade below the Friday's Sports Grill, just to the left of the Fatburger concession stand. It still might be rolling around out there with the ketchup and pickles.

Posey is a quiet guy by nature and doesn't take much overt credit for his accomplishments, but make no mistake about it, he was excited about his deeds Monday night. Long after the game was over, Posey stood watching the replay of his moon shot on a clubhouse television, enjoying every minute of it.

Asked how that felt, Posey simply said, "Good," leaving the media crowd wanting with the one-word answer.

"I do that to Henry, too, so it's nothing personal," said Posey, referring to longtime San Francisco Chronicle beat writer Henry Schulman.

Consider it Posey's idea of a joke.

"No, it felt good," he added. "I'd never faced [Reed] before, not even in Spring Training or anything. I was really just looking for a pitch, trying to get a pitch I could handle."

Unlike Posey, Reed wasn't admiring any replays of the way that particular at-bat ended.

"I haven't gone back and looked at it, but I missed my spot and he made me pay for it," said the D-backs' new closer. "I was trying to get inside and just left it over the middle of the plate. It was a terrible pitch and a good swing. Anybody is going to hit that a long way."

Posey, of course, isn't just anybody. At 27, he is the heart and soul of the Giants.

All the winning and his myriad contributions to it, beginning with an adroit ability to handle a complex and talented pitching staff, is self-evident.

The shattered ankle he suffered in 2011 on a play at the plate cost the Giants any chance of repeating as World Series champions. And ultimately that play started the revolution toward a rule change that has irrevocably altered a runner's ability to collide with a catcher positioned off the plate.

And last year, when in a single season Posey's numbers slipped from 24 homers to 15, 103 RBIs to 72 and that league-leading .336 batting average to .294, the Giants went from winning the World Series to losing 86 games.

The evidence may be a tad circumstantial, but it's pretty obvious that the universe the Giants play in resolves somewhat around Posey. That's how high the bar for him has been set, the bar Bochy was talking about.

"I think it's fair to say that Buster had a little bit of down year, not a real bad year," Bochy said. "We're not looking for him to hit for power. If he takes a good swing, it's going to leave the ballpark. It's going to be up to me to keep him fresh this year and I'll try to do that, but he can hit."

There are also those little, but other fairly significant things.

After the Giants had come back from a four-run deficit to tie the score at 7 in the seventh, the D-backs began to mount a counter-rally during the bottom of the inning. With one out and reliever Jean Machi just in the game, Cliff Pennington took off for second with A.J. Pollock sitting on two strikes. Pollock swung and missed. Posey whipped the ball down to second to nail Pennington for the key double play.

A player certainly can be measured by a game-winning homer or a strike-'em-out, throw-'em-out DP.

For Posey, it is all of those things. The Giants have opened on the road for five consecutive seasons. His contributions Monday night helped them win their first opener on the road since 2010.

"Really, it feels good to win our first game," Posey said. "It seems like we haven't done that in a long time."

But even more so, the greatness of a club and a player may be measured by whether they win their last game. And in that realm, as Posey goes, so go the Giants.

"Winning the last game," Posey said, "that's more important, don't you think?"