The Rotorua swimmer caught up as he and Grimsey pushed clear of the field before Radford unleashed a finishing burst to win in 35:15, with the Australian seven seconds back.
Kent held off Australian age champion Jared Poort for third place, with fifth fourth ahead of talented junior Stefan Talbot.
"It's a great feeling. It is one of the major swims in the country and so to make up for last year when I had a bad swim is a great feeling," Radford said.
"Considering how hard our training has been, to smash out a race like that is showing we are doing the right work and I can't wait for taper time when we are feeling refreshed.
"We had a normal week leading in to this with 10 sessions including yesterday and full gym. So to be able to swim like this off a week like that is great. I am feeling like nothing can stop me at the moment."
Baker was pushed to the limit in the women's race, after flying in from Queensland where she trains under Australian coach Denis Cotterell.
The 21-year-old and Webby locked into the men's pack including Stanley, Talbot, Kurt Bassett and top triathlete Graham O'Grady.
Baker showed her experience to turn on the after-burners to edge out Webby by just five seconds, winning in 38:30.
New Zealand's leading freestyler Lauren Boyle was third ahead of fellow North Shore clubmate Jessie Blundell.
"This win is important to me. The prize money is a big help for me to help towards paying my training fees which is a bonus,'' Baker said. "It's a good build-up towards Taupo which is important to us all as we fight for a spot in the Olympics so this is really important to us.
"I am still building up and not at my peak yet. Even at Taupo I won't be peaking because I need to aim to be at my very best in Portugal if I qualify.
"I am happy where I am at. I had some issues with my shoulder but everything seems to be back to normal and I am really pleased to get the win today. I love coming back to Auckland and to take part in this race is really special."
Results:
Men: Kane Radford (Rotorua) 35m16s, 1; Trent Grimsey (Australia) 35:23, 2; Steven Kent (North Shore) 36:12, 3; Jarrod Poort (Australia) 36:13, 4; Matthew Stanley (Matamata) 38:21, 5.
Women: Cara Baker (Howick Pakuranga) 38m30s, 1; Charlotte Webby (New Plymouth) 38:35, 2; Lauren Boyle (North Shore) 40:25, 3; Jessie Blundell (North Shore) 41:11, 4; Aimee Moss (Auckland) 42:12, 5.