Josh Hill won a chaotic first race where the red mist and a healthy dose of inexperience on a wet New Zealand track caught many of the drivers out.
Hill survived a heart-in-the-mouth moment that claimed Jonathan King and van Asseldonk towards the end of the race to take the win.
"It was surprisingly easy to control but it was a scary moment - I was on the radio shouting and swearing to my crew," said Hill.
Leitch and Jono Lester followed the Brit home.
Lessons had not been learned come race two with the safety car making an appearance every few laps, mainly because of unforced driver errors.
After the second race was declared early as the rain arrived, van Asseldonk crossed the line to win the Spirit of the Nation Cup, followed by Cassidy and Brazilian Bruno Bonifacio.
Race three was much the same with more safety car laps than race laps and was soon abandoned, with van Asseldonk taking line honours from Cassidy and Leitch.
Race one in the V8s saw Jason Bargwanna get one over the ever-improving Martin Short, who finished second after putting his car on pole for the first time, and Nick Ross rounded out the top three.
Series leader Angus Fogg fluffed his qualifying run and had to start from the back of grid and could only improve to fifth by race end.
Fogg made the most of his reverse grid position and won race two and was soon in control of the race, which he never relinquished.
Bargwanna soon came under attention from a hard charging Short who managed to get the inside line into the last corner before the chequered flag forcing Bargwanna wide and snatching second.
Bargwanna and Short continued their personal battle in race three with Fogg joining the fray as well early on.
Short gained control of the race after the pit stops only to make a mistake and let Fogg and Bargwanna get ahead. Not to be deterred, Short was all over the boot of Bargwanna but was unable to get past in the rain and had to settle for third.