The top-10 individual finish was a huge improvement on last year's 41st placing, when the youngster was laid low thanks to a crucial miscalculation.
"I got stomach cramps and walked from the far right corner," he said.
"I think I just ate too close to the race."
Harry was beaming at the prospect of a week off school and the chance to compete against some of the best young athletes in the country in a variety of events, but said triathalon would likely prove to be his sport of choice.
Low's feat is replicated by schoolmate Grace Blisset, who is listed to compete in multisport, swimming and hockey this week.
Christchurch's Lucy Kokich claimed the only individual record of the day, clocking 11m24s for the 3km distance, breaking the old mark - set in 2006 - by 4s.
Gisborne Intermediate's Briana Irving also dipped under the old record, clocking 11m 26s, but she couldn't head her Christchurch rival.
"I've been training quite hard but I didn't know how I was going to go today," Kokich said. "Just as I came up the last hill, I thought I could have a go and just had enough at the end."
Fairfield's Charli Miller was third in 11m 37s, also helping Fairfield win the Year 7 girls team title.
Another Hamilton athlete, Peachgrove's Kalyan Gujji, won the Year 7 boys, easing past Taradale's Ollie Marshall in the home straight, with Finn Seeds (Hutt International) third.
The Year 8 girls title also went south, captured by Liliana Braun (Christchurch South) in a time of 11m 25s.
Liam Back of St Peter's College won the Year 8 boys race.
Cross country results:
Year 7: Girls: Lucy Kokich (Cobham) 11m 24s (record) 1, Briana Irving (Gisborne) 11m 26s 2, Charli Miller (Fairfield) 11m 37s 3.
Teams: Fairfield 28 1, Otumoetai 29 2, Gisborne 35 3.
Boys: Kalyan Gujji (Peachgrove) 10m 56s 1, Ollie Marshall (Taradale) 11m 01s 2, Finn Seeds (Hutt International) 11m 07s 3.
Teams: Hutt International 25 1, Tauranga 29 2, Otumoetai 33 3.
Year 8: Girls: Liliana Braun (Christchurch South) 11m 25s 1, Phoebe McKnight (Hutt Intermediate) 11m 28s 2, Samantha Corbett (Pukenui School) 11m 44s 3.
Teams: St Margarets Chch 58 1, Otumoetai 62 2, Tauranga 83 3.
Boys: Liam Back (St Peter's College) 10m 26s 1, Finn Ward (Auckland Normal) 10m 28s 2, Matthew Proffit (Ilminster) 10m 30s 3.
Teams: Auckland Normal 16 1, Otumoetai 32 2, Tauranga 68 3.