As rust is not normally terminal in mature turf, N applications are advised to help the grass "grow out of it." However, rust can be very detrimental to new/young grass or turf in a weakened state. N is not a cure, it is intended to get the turf past/through that period when conditions are favorable to rust. Using the fungicide was the best choice for your situation.

Ok, that makes me feel a little better about using it. Thanks bud.

I would stick with nitrogen personally. Not sure where you live but I like beginning of sept, oct and then after thanksgiving for fertilizer.

Also, what is affected by the rust, the new seedlings or the existing lawn?

Northeast Ohio here. I'm going to throw down a synthetic tonight. I really try to go organic as possible but like I said I worked too damn hard on this overseed.

And the rust is friggin everywhere. I see the clouds of orange as I mow, and I'm bagging because of it....you should see how orange my bag is. Thanks for the reply, mishmosh.

NE Ohio here too. Maybe stressed out from heat cycling and lack of rain. Not having rust issues myself but new seedlings are certainly vulnerable as Ridgerunner mentioned.