CLEVELAND -- Now that it's over for the Chicago White Sox, the question must be asked:

What happened?

When daylight broke on Sept. 19, the Sox had won five straight to take a three-game lead on the Tigers in the American League Central. Both clubs had 15 left to play. The Sox's magic number was 13, and forecasts from Baseball Prospectus and coolstandings.com were both giving them an 83-percent chance of winning their division.

Math was on their side.

But then some ugly math began to get in their way.

Like the number 5.55 -- the Sox starters' ERA from Sept. 19 through Sunday, a span of 12 games.

And 1.5 -- the number of walks and hits allowed per inning pitched in that time frame, the highest WHIP among the contending clubs.

And .153 -- the Sox's batting average with runners in scoring position in that period, the worst such mark in the Majors.

And 2.58 -- the club's average runs scored in those 12 games, worst in the AL.

Yes, it took just 12 games for the White Sox to essentially unravel all the work that went into the 147 games that came before. It took just 12 games to turn a three-game edge into a three-game deficit, and that's all the more amazing when you consider they didn't face the Tigers in that time.

While the White Sox were losing 10 of 12, the Tigers were winning eight of 12. So when October dawned, the White Sox began their season-ending set with the Indians on the verge of being whacked.

The hit came Monday night, in the form of the Tigers' 6-3 clinching win in Kansas City. Chicago's 11-0 triumph over the Tribe was rendered moot, as was its season-long bid for the Central.

"We feel like we let one slip away," Jake Peavy said.

Indeed, the White Sox did. Because it's not as if the Tigers went on some ridiculous run to overtake them. Even if the Sox had won just six of those 12 games, they would have entered the final series with a one-game lead and a magic number of three.

"You're disappointed," manager Robin Ventura said, "because you were in a position to get in."

Maybe it wasn't quite as catastrophic a collapse as what happened to the Red Sox and Braves a year ago. But it was certainly an alarming fall from grace, given that Chicago had spent 117 days on top of the Central this season.

Of course, the context of this collapse is that hardly anybody expected the Sox to spend a single day atop the Central, let alone 117 of them.

To the Sox, that context matters quite a bit.

"There's no way you can say that because we didn't get in the playoffs it was an unsuccessful season," Peavy said. "It's a disappointing end to a successful season."

Yes, to contend as long as they did, with a new and completely untested manager, a younger roster and a few aging veterans coming off miserable 2011 showings, the Sox blew away the preseason projections. Ventura learned a lot about this club and a lot about the particulars of his new position. And Chris Sale, Jose Quintana, Addison Reed, Nate Jones and Hector Santiago, among others, all made huge developmental strides to make the future of the pitching staff look bright.

"Our young guys, there's too many to name," Paul Konerko said. "We've been in this all year because of how well they've played, a lot of them in their first year. It's hard just to make it through your first big league season. We had a lot of guys not only making it through but excelling in a pennant race. That's hard to find."

Really, this Sox team seemed to pull off the tricky feat of rebuilding and contending simultaneously. It wouldn't have been possible without Peavy, Adam Dunn and Alex Rios all having Comeback Player of the Year-type seasons. A club is lucky to strike gold in one such instance. Combine all three with Sale's transcendent transition to starting duties, mix in an underachieving Tigers team and an otherwise underwhelming division, and you had the rudimentary recipe for a revival.

For 5 1/2 months, it worked.

And then, these last two weeks, nothing worked.

Two losses in Kansas City, a sweep in Anaheim, defeat in two of three against the Indians and then three losses in four must-win games against the red-hot Rays.

All those innings seemed to catch up to the young arms. And while nobody questioned the effort or attention level, the Sox undoubtedly tightened up in some big moments.

Ventura, for one, said he wouldn't do anything different, from a personnel standpoint.

"You wish there could have been a hit here or there," Ventura said. "But as far as the people going in, trying to do it? No [regrets]."

Here's the organizational issue at hand: This subpar September was hardly a first. Since 2006, the Sox's record in September/October is a combined 93-107, giving them the fifth-worst such record in baseball in that seven-season span.

That's one issue for the Sox to chew on in the coming weeks and months. Another, more pressing issue is Peavy's contract status, as his $22 million option obviously won't be exercised. If the Sox can't configure a contract that appeals to both sides, there goes the established ace and the man who served as a mentor to Sale, among others.

Consider that the new focus, because the AL Central title is now out of sight. While it's true that the Sox challenged for that title ahead of schedule, the fact they had it in their grasp and let it slip away stings.

What happened here? The Sox will have all winter to think that one over.