Earles' first attempt at the long distance was at the off-road Motutapu event in Wanaka in March.
"I had a terrible race," he said of his Motutapu effort.
"I did three and a-half hours. It was sort of motivation for this one to try and put a good time together as I knew I had under-performed in that one."
Earles (26), a PhD chemistry student, won in a time of 2hr 48min 10sec.
He took a level-headed approach to the race around the Otago Harbour and appeared content to settle into second place behind Tom Hunt and not worry about the fact he was getting away from the field.
At the 10km mark, Hunt held a 35sec lead over Earles which blew out to 2min 18sec at the 20km mark.
"I just tried to set my own pace and not think about it too much," Earles said.
"It was a beautiful morning to do it.
I just tried to soak it all up and let the legs do their own thing and let the mind wander.
"That works until about the 30km and you really start to feel it, and then the focus kicks in. And you actually have to tell yourself to keep moving and count down the kilometres and really push yourself."
Earles was aware that around the 35km mark Hunt began to cramp up and, 1km from the finish, there was heartbreak for Hunt when Earles cruised past him.
"With 2km to go, I saw his little red tag, so I went for it," Earles said.
Earles admitted to feeling slightly guilty at not wearing his own red tag, signifying he was in the marathon and not the half marathon.
"I thought it would be a bit stink if I just ran past him [Hunt] and pretended to be a half-marathoner," Earles said.
"So I said, `Hi, how's it going?' to acknowledge him."
Hunt, who had held the lead from the start and was aiming for a sub-2hr 40min time, said afterwards it just was not his day.
Earles plans to take it easy for a while now and look towards next year's Peninsula Challenge.
Meanwhile, it has been a long battle but Sarah Chisnall appears to be over a stress fracture in her foot.
Chisnall (25), a phlebotomist (person who takes blood samples) based in Invercargill, controlled the women's section of the marathon from the start, completing the course in 2hr 51min 20sec.
The plan for Chisnall was to have a solid race and to just run it comfortably to regain her confidence following a disastrous return in June in the City of Christchurch marathon.
Her long-term goal is to focus on a good time in the Invercargill event on November 22, which doubles as the New Zealand championships.
"Christchurch was just terrible.
I lost it at 37km when my legs went.
It's good to just be part of it again and run on the home course," she said after yesterday's race.
Chisnall last won the Otago women's marathon title in 2006, going on to win the Canterbury marathon in 2007 before representing New Zealand at the world mountain-running championships in Switzerland.
She then started to suffer from the effects of a stress fracture in early 2008, while considered one of the most exciting prospects in New Zealand distance running at the time.
"It's been a slow process to get back to where I am now," she said.
"It's been a good year off without running, jogging, anything.
It's just fantastic to be back."
Second to finish the open women's section was Sue Cuthbert in 3hr 3min 8sec with Toni Smith third in 3hr 11min 5sec.
