"I kept looking back, just to make sure he didn't have anything else to give."
By the finish, Dunster had a lead of 30 seconds.
The first duathlon in the series had the same quinella and both events were part of Dunster's preparation for the Under-23 race at the ITU Cross Triathlon World Championships in Sardinia, Italy, at the end of September.
"I'll be doing most of the tri-series races over the summer, but I haven't got any target races yet - I just want to focus on the world champs in Italy. That's my biggest goal for the year. I've been training for about six weeks, getting fitter and getting faster. These local races are a training day really."
It isn't an explicit goal, but he said it would be nice to win all five races in the series.
"I'd like to, but it's a lead-up thing so if I don't win that's all right - they are club races I come to support."
There was also a repeat winner in the women's race, with Sarah Backler backing up her first race win a month ago.
She was tussling with male athletes for much of the second run, which led inevitably to a sprint finish.
"It would have been nice to not have had the sprint finish, but it's always good to have a few battles out there," she said.
Backler is also one of the New Zealand representatives at the ITU Cross Triathlon World Championships in September, and the duathlon series is also part of her build-up.
"For these races, it's really about going out and having a tough race - and you can try a few different things like pacing differently on the run or bike. You don't get battles if you're training [alone] so you just come out, go hard and have fun," she said.
For Southern Hemisphere athletes, the timing of the world championships wasn't ideal.
"Sardinia is really almost a prequel to the New Zealand summer, so you've almost got to peak for that then have a bit of a break without losing fitness so you can be ready for the New Zealand season."
She said that from a spectator point of view, it was disappointing to see that Auckland would no longer be staging a round of the World Triathlon Series.
"It's disappointing to be missing out on being able to watch that calibre of athletes there, but there are lots of other nice locations to go and do races in this country, so from that perspective I'm not too disappointed about it - but we are missing out on seeing top-quality athletes come and race."
Sunday's short course race was won by Blake Miller, with Olivia Cummings winning the women's race.