"I'm trying not to over run him but we will do Kihikihi and Sydney Three-day. I just have to keep ticking the boxes in the preparation for WEG [World Equestrian Games]."
Amanda Pottinger had a rail down with Just Kidding, to relinquish the runner-up position she had held from day one, while Johnstone had three down with Kate Wood's Wolf Whistle II, to drop out of contention.
"I was very disappointed. He has been clear at five of his last six rounds but he got a bit spooked at the practice fence and has not jumped in the premier arena before," Johnstone said.
Abby Lawrence also had a rail with Charlton Yamani, dropping to sixth, but Nick Brooks was over the moon to jump clear with For Fame and move into second place at the horse's first three-star start.
It was also was Brooks' first three-star finish, which was evident in his smile as he left the arena some time later.
Ashleigh McKinstry jumped clear with Pioneer Brass Monkey to take third place.
"I think he can go on to bigger things. He's been awesome here," said McKinstry.
Donna Edwards-Smith jumped clear on DSE Cluny to move into the money in fifth place, much to the delight of Cluny's owner, Gaye McClunie, who was watching nervously.
Lawrence won the CIC2* class on Anonymous, improving from second after the dressage to hold the lead after producing the fastest crosscountry round. Despite having a rail down in the showjumping, the margin was too big to lose the lead.
Su Jenkins, who asked Abby to ride him while she was out of action a year ago, schooled Anonymous.
The partnership was successful at one-star level, and Jenkins had agreed to sell the horse to Lawrence's mother, Raewyn.
Anonymous has now had four two-star starts. A proud and emotional Jenkins, who couldn't attend the show, had watched the drama unfold on live streaming.
Fleur Rohleder and The Alchemist improved from 10th after the dressage to be second after the crosscountry before showjumping clear to seal the runner-up position.
Dressage leader Samantha Felton, on Ricker Ridge Sooty GNZ, dropped to third after the crosscountry and also showjumped clear to hold that place.
CIC3*: Clarke Johnstone (Matangi), Balmoral Sensation, 40.5, 1; Nick Brooks (Cambridge), For Fame, 48.9, 2; Ashleigh McKinstry (Taumarunui), Pioneer Brass Monkey, 49.1, 3; Amanda Pottinger (Havelock Nth), Just Kidding, 51.2 4; Donna Edwards-Smith (Te Kauwhata), DSE Cluny, 51.9, 5; Abby Lawrence (Te Puke), Charlton Yamani, 52.8,6.
CIC2*: Abby Lawrence, Anonymous, 38.2, 1; Fleur Rohleder (Hamilton), The Alchemist, 44, 2; Samantha Felton (Matangi), Ricker Ridge Sooty GNZ, 46.3, 3; Rebel Morrow (Australia), Balmoral Henton, 50.1, 4; Donna Edwards-Smith, DSE Mendoza, 51.4, 5; Sophie Alexander (Auckland), World Famous, 52.8, 6.