Comically Bad

I WAS given a compulsory bye in round four, which may have been just as well considering how badly I messed up a simple finish today.
I won a pawn early on and exchanged off into a clearly won ending - indeed, for much of the time analysis engines reckon I am more than +50.

Position after 58.Qb5-b2 in John Nyman (146) - Spanton (167)

Somehow the obvious plan of putting my queen behind the a pawn never occurred to me. I have no idea why.
Instead I flaffed about aimlessly, blundered the a pawn for no compensation and reached the following position:

White has just played 72.Qb8-f8

For several horrible moments I thought I was getting mated.
Fortunately I collected myself enough to find a draw with 72...Qd5 (72...e2 also saves the half-point) 73.f6 Qh1+ 74.Kg5 Qd5+ 75.Kh4 Qh1+