Lynch (32), a former New Zealand triathlon representative from Porirua, had been prominent in her first two cracks at the title but luck had not gone her way.
She made a pact with father Mike to come back in a tandem team with him should she win the title.
"I guess I won’t be returning as a defending champion next year. I will have to honour my deal and race tandem."
Lynch was immediately in a tussle on Saturday with veteran star Simone Maier, chasing a sixth title, and Elina Ussher, aiming for a fifth.
First through transition at Aikens and on to the 33km alpine run stage, Lynch was proving a force up front, and only Moira Macdonald was able to match her as Maier and Ussher fell some 3min behind.
Macdonald made Lynch work hard on the long grind up Deception Valley and over Goat Pass, and nothing separated the two through transition at Klondyke.
Maier began to charge for the lead but the relentless pace up front was too much, and Lynch broke the tape in New Brighton in 13hr 6min 11sec.
Maier was second in 13hr 10min 30sec, and Ussher — in her 20th consecutive Longest Day race — finished third in 13hr 22min 28sec.
Lynch said she started to panic a little when things were not going completely to plan while she struggled to shake Macdonald on the alpine run.
When she decided to "just roll with it", she relaxed and was never really under threat, though she still had the odd moment on the bike home when she worried about Maier making a charge.
Lynch was delighted to win the title at her third attempt but mildly torn at playing spoiler to Maier’s hopes of winning a record sixth championship.
"Simone is just so amazing over this course. She is so strong.
"Last year I managed to bomb in the last 10km, so today I was red-lining the whole way."
It was a golden day for the coaching skills of multisport master Flavio Vianna.
Two of his multisport team members, Emily Trevail and Courtney Hawke, dominated the women’s two-day individual event.
Trevail, making the most of a 21min advantage from the first day, won in 13hr 14min 27sec, and Hawke was second in 13hr 33min 44sec.
Both marked birthdays in the days leading up to the event and can now relax and celebrate their efforts.
Trevail, 32, a fundraising consultant from Christchurch, hailed her large team of supporters and the support she got from training partner Hawke.
One of the stories of the day was the emergence of Sophie Shallard, from the small Southland rural community of Riversdale.
At just 21, and on the course for the first time, Shallard claimed third place in a smart time of 14hr 6min 20sec.
It came less than a week after finishing second in Southland’s 460km The Magnificent expedition race.
By Wayne Parsons
