Both teams were terrific, and the region was roaring. Baseball fever was running white-hot through the Bay Area, taking fans to the edge of ecstasy.
And now, a mere two games into the playoffs, the A's and the Giants are one loss away from being swept into an empty winter.
It's all so sudden, and the question on the minds of local fans, as both teams face elimination, reflects equal parts mystery and shock:
What the hell happened?
The convenient answer is that baseball is the most unpredictable of games, perhaps because it consistently presents the least forgiving of circumstances. A game can be decided at any moment, by a single bounce, in any inning, on any pitch between the first and the last.
That script more accurately describes the plight of the A's, who opened the best-of-five American League Division Series in Detroit and lost two in a row, both games tense and in doubt until the final pitch.
The Giants, meanwhile, entered the best-of-five National League Division Series with two home games, only to get rocked by Cincinnati, which looks like the best club in the league, if not all of baseball.
No matter how bleak the outlook -- and it's grave for the Giants -- neither series is over in any way, because it's baseball, where crazy things can happen. The fortunes of a team and a series can turn in an instant.
Yet, even as the longshot odds of a Bay Bridge series fade away, there are reasons for A's fans to be optimistic.
The A's are returning to the Coliseum, where last week they concluded the regular season with an incredible surge, overtaking Texas on the final day of the season and capturing the A.L. West division title.
The ballpark was a cauldron of energy throughout, and it will be abuzz Tuesday night when the teams take the field for Game 3 of the ALDS.
The Giants slog into Cincinnati facing an infinitely tougher task. They know there won't be another game at home this season unless they somehow win three in a row. And they've already been outscored 14-2 with their best starting pitchers, Matt Cain and Madison Bumgarner, on the mound in the comfortable confines of their bayside ballpark.
Of further concern to the Giants and their fans, though, is the disturbing truth that the 2012 team simply has not been very good against quality competition -- which describes the postseason field.
In finishing the regular season 94-68, the Giants built most of that against weaker opponents. They were 40-12 against the poor Rockies, Padres, Cubs and Astros. They were 54-56 against all other teams, including 11-15 against the other N.L. playoff teams: Atlanta, Cincinnati, Washington and St. Louis.
If the first two games against the Reds are any indication, the Giants simply are in over their heads.
Though Oakland sprinted into the postseason with a record identical to the Giants, 94-68, the A's have been more consistent in their play, regardless of the opponent. In putting together the best record in baseball over the final four months, it did not matter who was in the other dugout.
The A's this season were 24-21 against the other A.L. playoff teams: the Rangers, Tigers, Yankees and Orioles.
So which team is more likely to manage the epic comeback required to win its series and advance to the next round? That's easy. It's the A's.
Odds were against them coming into the season, and they've embraced their underdog role. They've had fun with it. They've used it to motivate and inspire, and to remind themselves and anyone willing to listen that even the smallest achievement will be perceived as a bonus.
In short, they've already won. And they know it, which is why the A's have the lowest pressure component of any team in the playoffs.
The Giants are the team with the MVP candidate, Buster Posey. They secured their postseason berth with 10 days to spare, allowing manager Bruce Bochy and general manager Brian Sabean to carefully assemble their roster and pitching rotation for the long haul.
All of that preparation has been reduced to one game, on the road, behind a starting pitcher, Ryan Vogelsong, who was superb for four-plus months but wildly inconsistent in the final weeks.
"It's not done yet," Bumgarner said in the wake of the Game 2 loss. "It's happened before, and teams have come back. It doesn't happen often, but it has been done."
Only once has a team lost the first two games at home and recovered to win a best-of-five series -- the 2001 New York Yankees, and they did it with Game 5 at home. They also did it against the A's, so if you believe in the baseball gods, the A's might be owed one.
Whatever your beliefs, the A's need to win three games in a row, beginning Tuesday night.
We know of baseball's double-edged allure, that the charm of the sport is its ability to lift your soul just as its curse is the way it breaks your heart.
But how dare the Bay Area baseball party stop now, so prematurely in our minds, when so many of us have spent weeks living it, anticipating so much more?