There was real interest in the men's race which attracted the strongest field of the series with all of New Zealand's main protagonists against some of Australia's best, including three- time national champion Grimsey and Great Australian Swim Series champion Michael Sheil.
The field was bunched until the midway point of the U-shaped swim around Rabbit and Leisure Islands before Grimsey put his foot on the accelerator.
"The pace until halfway was easy. I picked it up from there and the others fell off," said Grimsey. "I love swimming in the surf so catching a wave on the way in was all the better.
"Around the back of the rocks there was a bit of seaweed. That was a bit scary because I thought it was a shark. Other than that it was good. It was a great swim."
Radford, who is building towards the Olympic open water qualifying event in Europe in June, said the swim was good practice but he was still disappointed.
"I guess I wasn't all that happy in the end result because I always go out to win. But Trent is a classy swimmer and he had a classy swim today," said Radford.
"I was sitting really well in the middle stages and then I headed in the wrong direction and lost him from there. Once I was off his hip I had to work twice as hard and couldn't catch back up."
Radford, with two wins, a second and a third, retains his lead in the series but Grimsey can catch him in the next month's final round in Takapuna.
"I've done the math and think if I beat Kane by more than 10 seconds in the final round in Auckland I would win the series. I have another obligation that day but I am going to see if I can get out of it and come back."
Radford is under no illusions of the looming battle.
"The State King of the Bays is going to be a cracker if Trent comes back over because the title will be all on the line."
Webby, who is also preparing for June's Olympic qualifier, was delighted with her performance given the circumstances.
"It was probably the best swim course management that I've done. It was amazing out the back of Rabbit Island. Just coming in the buoy never seemed to get any closer and I caught a wave but dropped off it," said Webby.
"I guess it (my uncle) was the motivating reason for the good swim. I really, really wanted it for him more than anything. His family were here, and I went out there hoping for the best."
Queensland's Sheil finished third in the men's race ahead of triathlete Graham O'Grady and former national open water champion Philip Ryan.
Webby finished comfortably clear of Australian Tash Harrison with local surf lifesaving icon Johanna O'Connor third.
There were 800 swimmers competing in a range of swims including Blenheim man Peter Colbert, who made his comeback from a quadruple bypass last September.
The final round of the series is the State King of the Bays in Takapuna on March 31.
Full details and results: www.oceanswim.co.nz
