Given the starting rotation, which has had (and continues to have) so many question marks in it that it looks like the Riddler's backside, that the Yankees have locked up the American League East is an accomplishment in and of itself.
Of course, as good as the Yankees have been, they have been aided by Boston's nightmarish finish. On August 25, the Red Sox had just won their third game in a row, Andrew Miller pitching 6.1 innings of shutout baseball at the Rangers. Their record stood at 80-50 (.615), a pace for 100 wins. They were in first place, one game ahead of the Yankees. The next day they lost a 15-5 decision to the A's, which is very hard to do this year, and the roller coaster began its descent: in the 26 games since, they have gone 8-18. Their pitching staff, or what is left of it, has allowed 6.33 runs a game.
Injuries have more to do with what has happened than any kind of "choke," so I don't know if it's fair to infer any kind of moral failure in this collapse; Boston's sin, if any, is that they didn't have the depth to replace an entire starting rotation. Ninety-nine percent of teams don't (the Yankees do, though they won't use it). Despite my feeling almost sorry for Boston's best, I can't help but dedicate this tune to them...