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I nearly fell asleep on an LSR once.
Yeah, it's similar but you can do it by yourself and sober.
Agree with Sussex runner - there's no way the rest of the race was well paced and you took your eye off the ball between 7-9 miles! Doing that costs you a few seconds per mile, not a few minutes.
Whilst I agree that it is not sensible to go off ridiculously fast and crash and burn, to pace a race well, there are a few things you need to do. Firstly have a really good idea of your capability and target pace (check whether the race has km or mile markers and either write them down, or use a garmin etc to keep a check (remembering garmins etc and even race markers are not always correct!). Basically it is usually best to aim for a steady pace, so just divide target time by miles and try to stick to that. Having said not to go off ridiculously, I think to truly find out how good you can be, sometimes you have to take risks, set off a bit harder and be prepared for it to really hurt - it may mean you crash and burn, but sometimes you can hang on and do something better than you thought. I doesn't half hurt though!!
"I felt good all race really."
This is the bit which caught my eye.
I had a vision of the OP just cruising along in the comfort zone which isn't the place to be setting a PB.
However, I concede that you do need a fair amount of experience to really crunch a race, and a Half Marathon is a damn long way to race as a newish runner. You cannot help but be cautious.
Its relative really. The first distance I ever tried smashing was a 5k. I thought I could blast it the whole way since I'd already run a HM. Well it was a bit far to sprint but that's how I attacked it. The result was a 5:46 min mile average when I thought 6:15 was fast!
Two years later I blasted a HM because on the start line I remembered I'd spent the summer running 17 & 18 milers each Sunday. 13 miles! nothing.
You need confidence to eyeball these races. At 1:40 to 1:45 that's a long time for the OP to force the pace. Plenty of time to speed up and gain experience.