"Those boys really pushed me hard out there, so I give them credit, as it's something they don't normally do," he said.
Radford has now won this race five times from six attempts, and has ensured he's sent a strong message to his rivals, like Poort, and another Australian Rhys Mainstone, who'll be featuring in the series in the New Year.
"It's not an easy series this one. You can't just rock on up and win it," he said.
The women's race was far more clear cut with Taranaki's Charlotte Webby comfortably winning.
Webby was expecting a tough race with Wellington's Emma Robinson, a World Championship representative for New Zealand earlier this year, and talented Australian Jessica Walker.
But Webby made the race her own clearing away to win by 32 seconds.
"This is a huge confidence booster. To get a win is amazing. I know with sport it can be anyone's day on a given day, and today was my day."
In all, almost 1700 swam in the Harbour Crossing including several well-known names, with one being former All Blacks winger and now Blues rugby coach Sir John Kirwan.
He swam the race with former New Zealand triathlete Rick Wells, who helped Kirwan with his training regime. The pair finished in 51:06.
"I'm really happy. It was a fantastic experience. It was great swimming with Rick and I got into rhythm and enjoyed it.
"I'm a proud Aucklander. So, to be actually able to swim the Harbour that you've been driving around and looking at your whole life, is a real achievement," Kirwan said.