"I got a good jump off the line from an average gate pick on the outside," Whibley said.
"I ran deep into the turn and nearly took the holeshot but had to settle into second for a mile until I could push through to the front. Once in the lead I tried to go early as there was a large entry for this event and I knew lappers were going to be tough.
"I opened up a gap on [Australian former GNCC champion] Josh Strang and [American] Ricky Russell who were running second and third.
"About a mile or so from the end of the lap, I think I had maybe a 10 or 15-second lead, and my rear brake went out. I almost crashed twice, not being able to stop for turns and ploughed into the woods.
"I decided to back it down and pull into the pits when I could, to assess the problem. I pulled over and let Josh and Ricky by, then [Japanese rider] Takeshi Koikeda and Nick Bollinger came by too with Matt Nix and [fellow New Zealander] Callan May right behind me when I pulled off the track.
"Darrell Raines lent a hand and helped fix the problem, but by the time I rejoined the race I was a long way back.
"I decided to keep riding and complete the race, to get some good bike time before the GNCC opening round in Florida."
Aucklander May (Yamaha YZ250F) is living and training with Whibley in his debut US season.
"There would have been at least 500 people at this event," said May.
"It was crazy to see so many people at a race. I had a few small issues with my front brake but got that sorted, shook off my first-race nerves and ended up fifth overall, so I was pretty happy.
"I have been riding with Paul three times a week.
"It has been really good to see what it's like to not have to work fulltime and just ride."