My new sod looked great, then half of it turned yellow.

I spent a ton of money laying down new tall fescue sod this spring, and for the first three weeks, it was perfectly green. Now, a massive patch of it is turning yellow and looks totally dead, even though I've been watering exactly as instructed, about an inch every morning. I even aerated the area beforehand and put down some starter fertilizer. I found an interesting take on this over at JH Landscapes, that it might be a fungus issue and not a watering problem, which blew my mind because yellow meant drought.

Has anyone dealt with a sudden yellowing patch in new sod that wasn't fixed by just watering more? Specifically, what was the exact fungicide you used, and how long did it take to see the grass green up again once you treated it?