Cassidy and teammate Ryo Hirakawa gave the all-new Toyota GR Supra a win in its first race outing, with the marque locking out the top five positions at its home track.
It was a straightforward victory for the #37 pair, who started on pole and then survived two safety car restarts - the latter of which wiped out a lead of more than 20 seconds - to win by five seconds over the sister #36 TOM'S Supra.
#37 KeePer TOM'S GR Supra
The only time the #37 car came under any real threat as the first safety car restart, as second-placed Nirei Fukuzumi tried to launch an attack on Cassidy at Turn 1.
But the New Zealander said he knew the ARTA car - which finally faded to eighth - was running much softer rubber and wouldn't be a threat over a race distance.
"We knew they were on a very soft tyre, which warms up very fast," said Cassidy. "I knew before the race I just had to keep him behind for two or three laps.
"I was watching my dash to see where my tyres were at, I knew we were coming in [to the temperature window] soon, and after that corner I was able to start getting away."
Hirakawa inherited an 18-second lead from Cassidy, which was lost in the second safety car period, but he eased away from the sister TOM'S Supra of Yuhi Sekiguchi at the restart.
He said afterwards that he felt losing the lead he and Cassidy had built helped him focus.
"[The safety car] was unlucky, but I knew there were a lot of GT300 cars having trouble so I knew it was a possibility," recalled Hirakawa.
"Then again, with a lead of more than 20 seconds, I may not have been able to focus. We lost our advantage, but I think I was able to focus and drive well because of that."
Additional reporting by Tomohiro Yoshida
Ryo Hirakawa, Nick Cassidy（#37 KeePer TOM'S GR Supra）