"I had a mechanical issue and lost 18 minutes at Taupo, and after the 70.3 worlds I had hoped there was enough fuel in the tank to do well at the Ironman world championships but I blew up," Lawn said.
"I will now step into the preparation for Ironman New Zealand with a good win under my belt, knowing I am fit and injury free. That gives me confidence."
Lawn did not quite bury all of her ghosts, with a rear wheel issue halting her progress on the bike on Saturday, but once on the run she was able to put daylight between herself and fellow leader Belinda Harper, a former Hawaii age-group world champion.
"The rear wheel kept locking up so I stopped and thought it was fixed but it rubbed a bit more on the second lap. I just had to stay patient though and cope with it."
Lawn was the class of the field with the best swim and second fastest on the bike and run splits but said she never took victory for granted, despite the pre-race withdrawals of likely contenders Sam Warriner, Janine Sax and Anna Cleaver.
"These sorts of races you're generally against yourself and the distance anyway until it gets to that point in the race where you're racing each other but I don't own this race. Every time you toe the line it's a clean slate and today I won but next year maybe it's someone else.
"I like victories where it's a real race, like the battles I've had with Kate Bevilaqua and Anna, where you push it to the limit. It's not that enjoyable at the time but that's the art of racing."
Auckland's Hannah Lawrence, a latecomer to the sport four years ago aged 30, enjoyed the best run split of 1:28:23 to climb through the field to grab second, nearly seven minutes back, while Dunedin's Tamsyn Hayes was third.
"That's the best performance ever for me, I'm pretty happy with that," said Lawrence. "I've been working on improving my swim which was good today and I run strongly."
Lawrence was fifth off the bike, her best dismount position, with her goal over the next 21.1km to hold that spot. "I'd never gone into the run that far up before and I set about chasing down as many girls as possible." She moved into third at the 15km mark before overhauling Harper as they approached the base track for the second time.
The race was robbed of a likely challenger with former Mount College student Michele Bremer, recent Ironman Western Australia winner, puncturing early on the bike. She could not get the glued tyre off, losing nearly 15 minutes in the process and while she was strong on the rest of the bike and run, sixth was to be her lot.
"I was 2min down on Jo at that stage and adamant I wasn't going to DNF like I did here two years ago. Looking at my runs splits I was only 1min off Jo's time, so potentially I could have been up there challenging because I didn't exactly push myself on the run.
There proved only one in it, with Lawn the first female to win the Half four times, bettering the three titles won by Australian Rebekah Keat and Warriner.