This was the fourth marathon for Burnard, who runs for Wellington Scottish. He has done some barefoot training but mostly on grass.
Taking off his shoes in the heat of a road race was "a bit of a risk and in hindsight it was probably not the best idea", he said.
"It helped for about 5-6km, I got through to Mission Bay fairly easily but on the way back it started to take hold - and I had pains in my foot."
The result: "I can't really walk at the moment...I've got a few cuts and scrapes around my heels and toes, a few blood blisters as well but it wasn't too bad."
Burnard had hoped for an ambitious 2:30 time but after the knee injury decided he'd be content with a personal best.
He achieved that, with a 2:53 time against the 2:58 marathon he ran aged 17. He came in 25th overall.
The young runner said he's "pretty happy" with how he went, with many competitors finding Sunday's humid weather tough going.
Burnard has no fixed long-term plans for his running - he's just whittling down his personal bests across a range of race lengths to see how far he can go.
But right now he plans to take a month or so off running to recover.
And there's another bright spot - the spectator who took his shoes off him managed to locate him at the finish line. "She was nice enough to return them."