Is this heat stress or a fungus?

[micvog]

The past week has been in the low-90s with a 0.5" rainstorm. The lawn had some drought-stress near the end of the week, much of which has disappeared with another 0.5" of rain last night. However, there is a suspicious spot that looks like a fungus to me, but it doesn't match up exactly with the diseases I looked up at the MSU Turf Disease website.







I have had been aggressive with the N this Spring; cracked corn (20#/K) went down on 5/26, and Serenade went down (3oz/K) on 5/27 and 6/4.