Mr Sherlock's survival chances were rated at about 1 to 2 per cent, but thanks to the lifeguards' efforts he has made a full recovery.
"The type of cardiac arrest he was in, he was gone," Mr Malcolm said. "What [the paramedics] said to us was that the heart massage, the compressions that we did, sort of kept all the toxins out of the brain and kept the oxygen flowing through it so he didn't have any brain damage or anything. They were just amazed. He was up walking the next day."
It was Mr Malcolm's first resuscitation in five years of patrolling Gold Coast beaches.
"It was pretty intense," he said. "Lots of rib-breaking and lots of hard work. I've spoken to a couple of other lifeguards who have never got anyone back and had a number of resusses. He was really lucky that we spotted him early."
Exactly what happened to Mr Sherlock wasn't clear as he was pulled from the surf without having swallowed any water.
"From what we understand he pretty much swam himself to death," Mr Malcolm said. "He was a bit of an older guy. He wasn't ridiculously overweight but he was overweight and he just fully exhausted himself. He was in a really bad spot.
"I managed to flip him over within a couple of seconds then took him straight into the beach."
Mr Sherlock was taken to hospital but last week was well enough to meet the pair and say thanks.
Mr Malcolm explained there was never any question of stopping compressions, despite the bleak outlook.
"It was someone's dad, someone's husband, someone's granddad - we were just never going to give up," he said.
The 23-year-old is one of more than 950 lifeguards who will compete in this weekend's two-day Eastern Region championships, the second-biggest carnival of the year behind the national championships.
Surf drama
* Champion Kiwi surf lifesaver Nick Malcolm performed chest compressions on British tourist John Sherlock for 30 minutes, saving his life.
* The rescue was filmed by Australian news network Channel 9.
* The Gold Coast resident and Mairangi Bay club member will be back in New Zealand this weekend competing in the Eastern Regional championships at Whangamata.
On the web
Watch a Channel 9 clip of Nick Malcolm's heroics here: tinyurl.com/touristrescuers