After almost nine hours of swimming, riding and running, he had just 16 seconds to spare over his nearest competitor in the ironman event.

McDonald collapsed after crossing the line and needed a drip to re-hydrate in the 40-degree, 70 per cent humidity Kentucky conditions.

His father Neil spoke to him after the race yesterday.

“Chris said it was by far the hardest ironman he has ever done, he staggered to the line and collapsed,” he said.

“He had three drips in the first half-hour after the race just to recover.

“Chris has been training in the heat in Austin, Texas, to prepare for the race but he said there was nothing he could have done to prepare for the extreme conditions.

“Last year he went from this race to another at Lake Tahoe and won but I don’t think he will be able to do that after such a gut-busting effort.”

McDonald was fifth out of the 3.9-kilometre swim and third after the 180-kilometre bike leg.

“He took the lead in the run at the six-mile (9.65-kilometre) mark and ran on his own for another 20 miles (32.2 kilometres),” Neil McDonald said.

“That’s his seventh win in international ironmen races and that qualifies him to go to Hawaii, but that too is up in the air at the moment.

“He is just happy to have won as defending champion.”

McDonald told a US news service the margin didn’t matter, just the victory.

“To me it didn’t matter if I won by one second or 30 minutes,” he said.

“I had extremely low blood pressure and complete dehydration.

“There’s just no evaporation and perspiration to cool you down.

“Thankfully there was a lot of ice out there.”

Earlier this year, Chris, his two brothers and Neil, 67, made history when all four competed in the Houston Ironman.

The Albury boys’ ironman careers started with a mini-event at the Holbrook pool as kids.