He said he had to dig deep during the race after missing a few drink stations during the first half of the run.
"I was struggling around the back of the lake which used to be my favourite section of the course," he said. "I finally got one of my drinks [near Mourea]. I had missed them at earlier drink stations and couldn't be bothered turning around."
O'Callaghan said once he got some fuel back in the system he had enough energy to power home, peeling away from Kamijo.
He was happy to finish on the podium, he said, but would not give up his pursuit to win the marathon, after famously tripping close to the line in 2009 and losing out on first place.
"I'm definitely [entering again next year], this was just practice."
One marathon official said O'Callaghan was one of the toughest characters he had come across.
"He juggles work as a roofer, a young family and training and that's what makes him so tough - he's as tough as nails."
Meanwhile, Wreford said he was absolutely rapt with the win after entering the Rotorua Marathon for the first time.
"I started pulling away from Steve about the 13km mark. My plan was just to stay relaxed."
He said the course was a lot flatter than the terrain he trains on down south, which meant he could settle into a good pace.
Wreford said he was glad to have entered the race after considering missing the marathon following a recent injury.
"I was umming and ah-ing about whether I should do it or not but I thought I would just put my pride on the line and go for it."
After posting the best time seen at the marathon in 12 years, Wreford said he hoped to return next year and break the overall marathon record of 2h 16m 05s set by Paul Ballinger in 1988.
Other local runners also placed well at the marathon with Rotorua's Matthew Parsonage coming in fourth, Tokoroa's Adrian Lysaght finishing sixth and Rotorua's Sue Crowley finishing fourth in the women's marathon.
About 4000 competitors entered the 49th staging of the Lion Foundation Rotorua Marathon on Saturday.
