After victory in the first race, Carrick struck some problems in race two to finish 11th.
All the riders also had to factor in the wet and go a little conservatively.
"I think I could have taken [the series] if I finished up there more," Carrick said.
"We changed a few things on the bike for the wet I don't know what happened but I struggled.
"I'm not sure if it was the settings or me it is what it is."
Payne won the second race to go with his third placing earlier in the day, while Hassan's middle-order finishes gave him the Tri Series title by nine points.
"I know I made it difficult for myself by jumping in the deep end at Wanganui, but I had to ride here to have any chance of taking the title," said Hassan.
"I took it relatively easy and just hoped for the best.
"With Carrick winning the first race, I knew the pressure was on me to find some extra speed in the next race but it was a very tough thing to do.
"Thankfully Carrick had a few problems of his own in race two and I won the title."
For Hassan, the Tri Series was always more the warmup for the 600 supersport class in the national this season.
That five-round series set to kick off at Ruapuna on January 5-6.
Budget reasons means Carrick cannot race the whole series but will take part in the North Island rounds at Hampton Downs and Taupo.
But he will definitely be lining up again in the Formula 2 class in next year's Tri Series with the plan to go one podium spot better.
"I rode a little bit last year but this was the first proper season.
"I wasn't expecting to do that well but I'll take it, that's for sure.
"It's just about having the right set up on the bike and a good qualifier get them right and you go for it really."
Carrick's Suzuki GSX-R600 bike was ridden last year by Dennis Charlett, who stepped up to claim the Formula 1 title in Wanganui.