"I swam pretty well for me. I was probably about eighth out of the water and I felt really good on the bike, I felt really strong.
"Whenever there was a hill I managed to overtake someone and I took the lead about half way through the bike.
"It was the best I have ever cycled in a race before."
Supporters from the Rotorua Association of Triathletes and the Lake City Athletic Club were at the finish to cheer him home.
"It was good to have some home town support," he said. "I think it is always good if a local can win a fairly big event [at home]."
The victory was Parsonage's first at a recognised half ironman event.
As tradition would have it in the Rotorua Half Ironman, Parsonage received a giant teddy bear for winning the race.
He also recorded his personal best time on Saturday at Lake Tikitapu (Blue Lake).
The 33-year-old said he was looking forward to defending his title next year.
Meanwhile, the women's race on Saturday was won by Waikato's Wendy Nicholls, who has won the women's race before in 2011.
Race director Shane Hooks said the hot weather made the race even tougher for the 500-plus participants.
"The heat combined with the difficulty of the course made it a particularly hard day, but that added to the satisfaction for participants," he said.
"It was close to one of our best ever [events]. We didn't have a single bike accident which is one of the biggest things for us, having a good safe race."
Hooks praised the performance of Parsonage, who had entered the race during the past three years.
"He is a great amateur ... it is very hard for an amateur now days to get to the top, but he got there," Hooks said.
Meanwhile, an hour down the road, Taupo's Graham O'Grady showed why he is one of the best pro triathletes in the country. O'Grady won the Taupo Half Ironman in a blistering time of 4h 0m 28s to defend his title from 2012. O'Grady also won the Rotorua Half Ironman in 2010.
The women's race in Taupo was won by Cambridge's Candice Hammond.
