Don't look now, but Alfredo Aceves has passed Ian Kennedy on the Yankees' prospect list. The two pitchers are very similar. Both are right-handers of unexceptional stature with similar repertoires (91 mile per hour fastball, changeup, curve). Both went from high-A to the major league rotation in their first year of pro ball, and both have impressed in their September call-ups.

The difference between the two is that Aceves did last night all of the things the Yankees have been trying and failing to get Kennedy to do all season. He threw strikes, worked quickly, and mixed in all of his pitches. That last is the most significant. In his various unsuccessful stints in the major leagues this year, Kennedy has been a two-pitch pitcher, throwing straight fastballs to spots (and often missing) and trying to get his outs with his changeup. Last night, Aceves varied speeds and breaks on all three of his pitches (really four as his best pitch is a cut fastball with some impressive movement) giving him an assortment several times more varied than Kennedy's.

Of course, Aceves maturity on the mound comes from his maturity off it. Aceves may be in his first year of "pro ball," but he has six years of professional experience in the Mexican League behind him while Kennedy was pitching in college in 2006. Despite that, Aceves is just two years older than Kennedy. It's possible that Kennedy could learn what Aceves knows in the next two years, but even if he does, he's unlikely to be much better than Aceves is now. The real question is exactly how good is Aceves now? He'll certainly be in the mix for next year's rotation, but is he just a younger, wilier Darrell Rasner, the sort of pitcher who can fill a vacant rotation spot and slide back into a long relief role when the rest of the starters get healthy, or does he have the potential to be a mid-rotation guy like many hoped and even assumed Kennedy would be as early as this year?

Whatever he is, it's worth recognizing that in one short season he's passed fellow 25-year-old Alan Horne, Jeff Marquez, and even Kennedy on the Yankees' list of starting pitching prospects, which may tell you as much about Horne, Marquez, and Kennedy as it does about Aceves.