With a large transition area, it was still difficult to gauge where she was in the field.
"I spend the whole run trying to find other girls with 25 on their leg - but I didn't manage it because I was in front."
There was a clue when she caught runners from the 20-25 age group - and she managed to put in a personal best for the 5km run - but she really had no idea she had won her age group when she crossed the line.
"I don't wear a watch in a race, I just go with how I feel, so if I feel good, I race harder. I
don't have anything telling me I need to run faster except my mind.
"My dad was there with me, and a few friends were there and they came and said 'good work, but we've no idea where you've come. You may be first, or you might be third'."
In the end it was one of those friends who saw the results first, but McNearney sent him back to take a photograph of them before she believed it.
The championships took place on the island of Cozumel, which has hosted three consecutive ITU World Cup events. McNearney knew heat was going to be an issue.
She travelled to Mexico two weeks before the event, spending a week in Cancun before heading to Cozumel.
"It was 30 degrees and 80 per cent humidity. The first day I arrived, I tried to do a run and struggled to cover 3km. Living in Hamilton, nothing could have prepared me for that.
"Even if I had put on few layers and tried to do a training session, I don't think it would have been the same.
The training in Cancun focused on swimming and running.
"There was nowhere to bike, but the running was so important because I guess that's what's affected most [by the heat]. Sitting on the bike, you have water available.''
Conditions were a little easier to bear on Cozumel.
"I got to train on the course and to go around the island and had a few training sessions with other Kiwis. It was a little bit cooler in Cozumel. It's an island just off the coast and there are sea breeze that come through.
While pleased with the result, McNearney said her first thoughts were of her next challenge.
"I think as an athlete you, look at it and think 'cool, I got a gold', but then I'm like 'what's my next goal?'. That starts to take over, rather than looking back.''
Her next goal is to move up to the longer, Olympic, distance triathlon.