Scheduled is one thing, charter is another, IRROPS another, and test flights yet another.

I am surprised that DL would land a 757 at MKC. DL has no ground services there, and although the runway may be able to handle it (I have seen a few other big jets land there), MCI would seem to be the logical choice. Further, whether the Sox were coming or going, if you accept the proposition (and I have no reason to doubt it) that DL was willing to go into MKC, why wouldn't the Sox take the bus to/from MKC, which is closer to "The K" than is MCI. On the other hand, maybe the charter went into MKC, and the Sox were going to be there for awhile, so DL sent the plane up to MCI for some other purpose. And MCI isn't all that much further from the stadium, and traffic and speed limits are better on the way to MCI.

Anyway, back to the shortest flights, I am pretty sure that way back when, UA flew OAK-SFO. As for me, I've flown BOI-BOI, DFW-DFW, & PHL-PHL due to mechanicals and weather, but each of those was probably over 100 miles. If you want to see some interesting flights that appear to be zero miles, check out the Boeing test flights on Flightaware that originate and end at PAE.