Russian driver Dimitry Suranovich took advantage of the reverse grid top six race and held off the chasing pack of Cassidy and company to get his first podium of the series.
Big mover of the weekend was another Kiwi, Jono Lester, who arrived an unfamiliar 12th on the table but rocketed up to fifth equal in the standings with an eighth and two fourths.
In race two the leading pair of Bruno Bonifacio and Hannes van Asseldonk came unstuck at different times, letting Cassidy slip through to take the lead and win from Puerto Rican Felix Serralles and Brit Jordan King.
"Right from the start I could see the track was going to dry out," said Cassidy. "The other guys around me were racing pretty hard so I just had to look after the tyres and that was the key really."
Co-leader in the championship after four races, Leitch was in the hunt early on only to overcook it going into the hairpin and had to settle for fifth.
"I just locked up the back wheels and ran pretty wide out onto the grass. It was hard to recover from that to come back to fifth, which is not too bad."
Angus Fogg continues his inexorable march towards his first BNT NZV8 championship win with a commanding performance at Timaru. He put the rest of the field to the sword with two wins and third to lead the championship from Australian V8 Supercar driver Jason Bargwanna and find of the series Martin Short.
In the third race the Aucklander cleaned out the field by half a lap.
"It's been a fantastic weekend and we've been pretty dominant," said Fogg. "We're better placed than last year but we've only had average rounds at Manfeild and Taupo [next two events] in the past."
Nick Ross made the most of the reverse grid second race and went on to claim his first V8 race win and was followed home by Short and Fogg.
