The victory adds to a remarkable sequence of success for Meffan. Since he finished second in the Edmond Cup steeplechase in June, he has won both the Otago cross-country and road titles, and claimed his first national medal, bronze at the national road championships in Wellington last weekend.
"I wasn't really running on fresh legs," he said.
"I just tried to tuck in a little bit and tried not to spend to much energy early on."
Meffan was embroiled in a three-way battle with former champion Dougal Thorburn and 2009 Otago cross-country champion Nathan Baxter over the first half of the course, until Thorburn pulled away and opened up a 100m lead.
Meffan, feeling a surge of energy just before the 19km mark, began to gain on Thorburn and overtook him 1500m from the finish.
"I wasn't really expecting to win," Meffan said.
"Dougal was just so strong, particularly between 10km and 15km."
Meffan's next target is the national 10km track championship in Timaru later this year.
"It's been a pretty amazing season for me so far. It's a nice way to finish off the road season with my first ever half-marathon."
Meffan targeted a time of 70min for the event, breaking the tape in 1hr 9min 50sec, a full minute clear of Thorburn, who clocked in at 1hr 10min 51sec.
Baxter was 24sec back in third.
It has been a long wait to see Shireen Crumpton back on the winner's podium at the Dunedin event, but she made no race of it yesterday.
Crumpton built on an early lead in the women's half-marathon to cross in 1hr 22min 25sec, comfortably clear of Louisa Andrew (1hr 26min 2sec) and Sasha Antunovic (1hr 27min 30sec).
Crumpton last ran the event when it doubled as the national half-marathon championship, winning that in a quicker time of 1hr 15min 3sec.
"It's good to be back," she said.
Crumpton faced the surgeon's scalpel last December for a damaged Achilles and the removal of bone matter from around her heel.
Only over the past two weeks has she been able to run without any Achilles discomfort.
Crumpton, whose 2004 time remains a record for the event, said her only major worry yesterday was dealing with the wind, which was swirling around the bays.
"It was pretty brutal, actually."
Crumpton has a number of goals for the coming months but is waiting to see how her training progresses.