The Giants started their biggest series of the season Thursday night at AT&T Park. The four-game set pits two of the top three contenders for the National League wild-card spot against each other, and could play a huge role in deciding who plays on and who goes home at the end of the season.

From a historical perspective, there's even more at stake. If the Giants stumble in this series against the Cardinals, and lose out to the Cards and Mets in the NL wild-card race, they'll have pulled off an ignominious feat: one of the biggest collapses the sport has seen in more than half a century.

By winning the opener of the four-game set against St. Louis, the Giants improved to 21-35 since the All-Star break, the worst record in all of baseball. By contrast, the Giants surged to a 57-33 record in the first half, the best record in all of baseball by a full three games.

To put that freefall into perspective, let's turn to our friends at Baseball Prospectus. Going back to 1960 (just before the start of the expansion era), BP researcher John Choiniere ranked the biggest collapses based on the biggest gaps in winning percentage from any point in July or August of a season, until the end of the season.

We used these parameters because of sample size. It's far easier for a team to put up a wildly aberrant record over the course of a few days or a couple weeks than it is to do so over a month or two (or three). This also better captures what's going with the Giants, who aren't in a short and hideous little slump, but rather a brutal freefall that's lasted two months and counting.

It also disqualifies several September collapsers from contention. Those include the 1964 Phillies (led the NL by 6 1/2 games with 12 games left in the season, then lost 10 in a row(!) to finish in a tie for second); the 2007 Mets (led the NL East by seven games on Sept. 12, went 5-12 the rest of the way to miss the playoffs by one game); the 1987 Blue Jays (led the AL East by 3 1/2 games with seven to play in the season ... lost all seven and missed the playoffs); and the 1978 Red Sox (Bucky f'ing Dent -- you should probably not click this link if you're a Sox fan). Since the reliability of BP's database and game logs improves starting in 1960, we also miss out on the 1951 Brooklyn Dodgers, who blew a 13-game mid-August lead, then got eliminated on a home run you might have heard about.

If we stick to July and August records as the starting point, the biggest collapse of the past 56 years belongs to ... the 2002 Orioles, who went an even 63-63 until August 23 of that season, then an apocalyptic-ly awful 4-32 thereafter. That example doesn't quite capture what's happening to this year's Giants either though, since the '02 O's were a long shot to make the playoffs with a .500 record that late in the season.

So while we can slice and dice these data in a bunch of different ways, we came up a quick and dirty way to do it here: Any team in the wild-card era (1995 or later) that was leading its division or a wild-card race when their collapse started (at some point in July or August), or any team in the pre-wild-card era (1960-93) that was leading its division when their collapse started, qualifies for our list.

With those parameters in mind, let's see how a 2016 Giants collapse ending with them missing the playoffs would compare to the biggest late-season swooners of the past 56 years. Call them the slow-death squad.

Dishonorable mention: 2016 Blue Jays

Before August 31: 76-57 (.571); after August 31: 3-9 (.250)

This result is heavily influenced by small sample size, with the Jays' futility lasting just a couple weeks. Still, with Toronto falling out of first place, now in third and struggling just to hang onto the lesser of the two wild-card spots, the Giants could have company this year in the folding-down-the-stretch department.

5. 2011 Braves

Before August 25: 79-53 (.598); after August 25: 10-20 (.333)

An American League counterpart would gain more notoriety for its own collapse, but the 2011 Braves suffered plenty of their own heartbreak. On August 25 they trailed a loaded Phillies team by six games in the NL East, but still held the second-best record in the National League, and a massive 9 1/2-game lead in the wild-card race.

Even after suffering through a terrible month, the Braves still seemed to have a playoff spot locked up late in the season. With just five games left to play, they led the Cardinals by three games in the wild-card hunt. They then lost their next four games, falling into a tie with St. Louis heading into Game 162.

Even then it seemed like they could still salvage their season, taking a 3-2 lead into the ninth inning against a Phillies team that had long since clinched the division title. But a Chase Utley sacrifice fly tied it in the ninth, and a Hunter Pence dying-quail infield hit in the 13th drove the final stake through their heart.

Many have called Sept. 28, 2011 the craziest night of regular-season baseball ever. The Braves just ended up on the wrong side of history.

4. 2014 Brewers

Before August 19: 71-55 (.563); after August 19: 11-25 (.306)

Probably the least notorious collapse on this list, the 2014 Brewers still blew a golden opportunity in spectacular fashion. A five-game winning streak in mid-August helped them open up a 2 1/2-game lead in the NL Central.

Typical of many late-season swoons, the Brewers rolled up a big losing streak, dropping nine in a row (and 13 of 14) from late August into early September. By season's end, they'd tumbled all the way to third place, barely finishing above .500.

3. 1969 Cubs

Before August 31: 83-53 (.610); after August 31: 9-18 (.333)

Skippered by legendary manager Leo Durocher and featuring four future Hall of Famers (Ernie Banks, Billy Williams, Ferguson Jenkins, and Ron Santo) the Cubs led the newly formed NL East for 155 days during that 1969 season. They led the division by 4 1/2 games at the end of August, and bumped their lead to five games on Sept. 2.

That's when the losing started. The Cubs lost four in a row against the Reds and Pirates, traveled to Shea Stadium, and got swept in a two-game set by the team that would pass them in the standings, and come to be known as the Miracle Mets. All told, the Cubs would go on to drop 17 1/2 games to the Mets in the final quarter of the season, marking one of the most disappointing seasons in the history of baseball's most disappointing franchise.

2. 1995 Angels

Before August 15: 64-38 (.627); after August 15: 14-29 (.326)

The Halos didn't merely lead the AL West by 10 1/2 games on August 15, 1995. They were surface-of-the-sun hot, having gone 25-8 since the break.

Then everything fell apart. Over that final month and a half, the Angels suffered through not one, but two nine-game losing streaks. The second skid wiped out the six-game lead they held in the AL West with just 17 games left to play, swinging the division to the Refuse To Lose Mariners.

The final blow came on Oct. 2, when Randy Johnson and the M's beat the Angels in a play-in game to end the regular season. The Kingdome ... got a little crazy.

1. 2011 Red Sox

Before August 31: 83-52 (.615); after August 31: 7-20 (.259)

Robert f'ing Andino.

Dan f'ing Johnson.

And Evan f'ing Longoria.

In the mad rush by ownership to vilify as many of the protagonists as possible, and certain Boston media members' eagerness to serve as stenographer for the owners' wishes, a huge piece appeared in the Boston Globe on October 12, 2011 (two weeks after the Andino game). The supposed expose claimed that the players were too caught up in fried chicken, beer, and video games, and the manager (Terry Francona) too hooked on pills for the team to stay upright (never mind that the team got clobbered by key injuries, and that the Rays deserved credit for playing terrific baseball down the stretch to catch them).

That same day, Theo Epstein jumped to the Cubs, signing a five-year, $18.5 million deal to take over their baseball operations department. If the Cubs go on to win the World Series this year and end their 108-year drought, the Red Sox collapse of five years earlier will have played a significant role in making that happen.

At their current pace and based on our guidelines, the Giants would rank as the sixth-biggest collapse since 1960. After Thursday's win against the Cards, they sit 1 game ahead in the wild-card race.

San Francisco's bullpen has absorbed a ton of blame for the team's woes. And while Santiago Casilla does lead the NL with eight blown saves and did enough damage to lose his closer job, the pen overall hasn't been all that bad in the second half; in fact, Giants relievers have gone from a 3.94 ERA before the All-Star break to 3.25 after.

Instead, it's the offense that's been their undoing. Before the break, the Giants collectively batted .263/.336/.406; adjust for the pitcher-friendly environment of AT&T Park, and that was the eighth-best mark for any team in the majors. After the break, they've slipped to .248/.319/.387, ranking 22nd in baseball in park-adjusted offense.

Some of their best players have been the biggest culprits: Brandon Belt's batting just .221/.357/.365 since the break, while Buster Posey has just one home run in the second half, backing up GM Bobby Evans' recent assertion that he's been playing hurt for much of the season, even though the Giants and Posey haven't offered any specifics. The picture gets even more grim if you look the Giants' September results, with the team batting a brutal .217/.288/.339 so far this month.

Still, if you're a Giants fan looking for a silver lining, there's this: In the first half of this season, the Giants benefited more from big hits in high-leverage situations than all but two other teams, winning three more games than they would have had they produced average results in those spots (according to Fangraphs). In the second half, they've been ludicrously unproductive in those same high-leverage spots, losing four or five more games than you'd expect given average results.

The Giants obviously didn't suddenly go from being a bunch of clutch gods to being chokers incapable of stepping to the plate in a big spot without their knees knocking. Rather, this amounts to a simple case of random chance, or plain old bad luck biting them in the ass. The thing about any extreme version of luck -- good or bad -- is that eventually it tends to regress toward the mean.

The biggest question, then, is when that might happen. If the Giants have even an ounce of #EvenYear mojo left, now would be a great time for it to show itself. If not, they could end up on the saddest of all baseball lists.