Tyler King, 13, is Omokoroa's other player at the age group champs.
Middleton will play in the under-15 division of the age group tournament, with 18 holes on Wednesday and Thursday followed by a cut for the top-72 players before Friday's final round. Past winners of the under-19 title include Aussies Jason Day and Adam Scott and Kiwi Michael Campbell.
Omokoroa's new blue tees will be in play on most holes, stretching the course by 400m out to 6236m.
If there's no rain in the next few days Middleton predicts the scoring could be hot. But the extra length could prove to be a significant judder bar, even for the testosterone-fuelled bigger hitters who show no fear with driver in their hands.
"Everyone probably thinks some of the better guys will tear a place like this apart but those blue tees make the course heaps harder - it's all carry and no run and you're having to fly the ball the whole way.
"In the summer out here it's quite different because the ground is harder and you can't just aim anywhere you like. In winter you need to stay out of the areas that get super wet so par could be a good score if it's soft underfoot."
Middleton emigrated with his parents from Britain five years ago and joined Omokoroa, with his first handicap a barely imposing 38. Lessons with coach Mikki Strong saw the Katikati College Year 10 student's index plummet. He's now down to five, cutting a whole nine shots off his 14 handicap from a year ago.
"There were three of us when I started playing, all about the same level, but I practised more and got better quite fast which made me realise the more I put into it the more I'd get out if what I was doing was quality."
Strong said in many ways Middleton was a typical teenager, "possessing a huge amount of passion for things," but was different to a lot of his peers.
"He's got a lot of potential and has a strong work ethic, although that alone isn't unusual with kids who haven't been playing the game for long and have got good quite fast," Strong said.
"What makes Harry a bit different is that he relishes rather than backs away from a challenge. He'd rather go out and have a game than spend a couple of hours bashing balls on the practise range, but even then there's an edge to what he's doing.
"You only have to look at his results in the championship pennant so see the more pressure that was applied the better he was,"
Middleton broke 80 for the first time a year ago, was a rock for the club's championship pennant team, losing just once in singles at No 8, and made his debut for Bay of Plenty last month as a late ring-in, halving his match in the win over North Harbour.
He bikes to Omokoroa after school each day, spending at least 2 hours playing or practising, and is a fixture at the club all day every day during the school holidays.