Over at SI.com Cliff takes a look at second-half X-factors who could decide playoff chases. First up, that man Joba:

On Tuesday night, Mariano Rivera announced that he’s going to skip the All-Star Game due to some minor injuries. Rivera has been pitching through the pain and doesn’t expect to go on the disabled list, but he’s unable to pitch more than one inning per appearance, and Yankee manager Joe Girardi has to be extra careful with the 40-year-old’s workload. That means Chamberlain, whose frustrating inconsistency has followed him back to the bullpen, will not only have to get out of his own jams, but could be called upon to close at points in the second half (he has already picked up two saves in the first half). While Rivera has been his usual dominant self thus far, the rest of the Yankee pen has been struggling, hurt, or both (see: Park, Chan Ho) for much of the season. Chamberlain dominated out of the pen before the Yankees moved him into the rotation in mid 2008 (1.32 ERA, 12.1 K/9 in 47 2/3 IP). In an AL East race in which the three best teams in baseball are separated by just three games and at least one will miss the playoffs entirely, Chamberlain needs to find that old consistency and fast to help ensure that the reigning world champions will be back in the playoffs to defend their title.