Well... it didn't!
It was boringly mundane, in fact. Felt strong and the legs held out well (such a difference from when I started running 6 weeks ago!). 25 miles, the first 20 at 9:02 pace at 145 heart rate. A fraction slower than what I was hoping for, pace-wise, but getting there.
Saw an over-excited dog knock its owner over. Got annoyed by some tourists shambling randomly over the pavement. Accidentally cleared my sinuses on a cyclist's leg. The usual, really.
Haven't developed any mosquito superpowers yet, from yesterday's bites.
The curve has definitely flattened out, but that was only to be expected. Up to 2 weeks ago, we would have extrapolated a 2:30 marathon by January(!).