Hesketh went through "all the grades", played Ross Shield primary schools' tournament rugby after having to resort to a motel sauna to get below the weight limit, and played in the Napier Boys' High School Under-15 team when it was second in the 1999 national final, and in the First XV when they won the Super Eight schools title in 2002.
But it had almost always been as a flanker, until the First XV became short of backs on a tour of Argentina, and tried Hesketh on the wing, said Del Whyte, who was to coach the side with fellow teacher Stu Gourdie.
At intermediate school, Hesketh had had to choose between rugby and gymnastics, his nanna said, and at Boys' High he also excelled as a track and field all-rounder, winning the school's Intermediate athletics championship.
He headed south to study physical education at Otago University, playing for Alhambra Union club and making his way into the Otago side, making his debut as a substitute against Hawke's Bay in 2006 and ultimately playing 35 games for the Dunedin-based union.
Unable to gain a Super rugby contract, he decided in 2010 to try his luck with Manukata Sanix Blues, in Fukuoka, and after becoming eligible to play for Japan last year made his international debut against the Maori All Blacks in Kobe in November.
His first test was in a win over Romania in Bucharest two weeks later, and he scored the first two of his now seven test-match tries in a loss to Georgia on November 23.
His nanna doesn't believe it would have worried him that he didn't get a run-on start in his team's World Cup opener.
"I think he enjoys being the impact player, and he's done what they wanted him to."
Knowing he'd had a sore back, she wasn't too sure she would see him, but then came the moment, the ball spinning left to the man in red-and-white jersey No23.
"That's Karne Hesketh, from Hawke's Bay," Mrs Pettit remembers a commentator saying.
"I was shocked," she said. "I was amazed that they beat South Africa."
Among those in Brighton to watch the 34-32 win were Hesketh's mother, Christina, a social worker in England who rang home soon after the famous triumph.
But "Nanna" was confident that sooner or later she'd hear from the player.
"He will ring me," she said, though she knows he has a busy time ahead.
She said he was planning to be back in Napier for a short time after the six-week cup tournament.
Hesketh was born in Napier and turned 30 last month. He and his partner, New Zealand women's rugby representative Carla Hohepa, have a 3-year-old son, Cohen.