Waddell was working a higher line and built the momentum to challenge Osborne, edging ahead for a few moments on lap seven with a full power outside pass but then running too wide in the next corner, allowing Osborne back in front.
Harding also raced the higher line on his way forward from grid five to pass Waddell and also made it work for a move on Osborne which put him in front for a moment on lap 16.
Osborne regained the lead and had control in the final part of the race.
"I knew Dean was probably going to be the one to beat," said Osborne.
"I had to get out of the first corner ahead of him. After that everything went to plan. Ben had a couple of sniffs as well but we had set up the car for later in the race."
Waddell's move to the outside line wasn't by choice.
"We were supposed to be on after the sprint cars and I thought they would dust off the track," said Waddell.
"But they bumped us up before them and the car was too tight - I just couldn't get it to turn. Once I got past Mark I should have dived to the bottom and tied to shut up shop."
For Harding, the outside was a choice but he eventually decided he couldn't persist with the faster but much rougher line.
"The car and I were really taking a beating up there. We were bottoming out and cushion was about a foot high in places. Then Dean moved up on me and it put me into the wall. I lost my momentum after that."
Corin repassed Harding to complete the podium.
"It was really cool to race with those guys. You can see the horsepower that Dean and Ben have got, they come up alongside you and they're really singing," Corin said.
Harding was fourth, ahead of Tauranga's Karl Hanlon, who produced a strong performance in his new car, with Nelson racer Ian Burson sixth.
With the 10pm curfew closing in, the BOP Sprint Car Champs was shortened from the scheduled 25 laps and with 14 completed it was Aucklander Jamie McDonald out in front but beginning to come under pressure from Mt Maunganui's Brad Tyrrell.
McDonald had started from pole position after a third place in heat one and a thinking drive in the marathon second heat which saw numerous incidents.
"The second heat was a race of attrition. We used our experience, put on plenty of (visor) tear-offs and put plenty of fuel in the car," said McDonald.
"Guys were running out of fuel. I got through from the back to finish sixth and put it on the front row for the feature."
Tyrrell's result was a boost after a troubled early season run.
He said one relatively minor change to the car had restored his confidence.
Third went to Tokoroa's Keaton Dahm, his meeting-by-meeting emergence as a consistent front runner rewarded by a podium against a high-quality field.
