Competing in a very strong field, Johnstone and Callister advanced to the 10-man final in fifth and tenth places respectively.
Both athletes put down two of the three runs in the Final, but were unable to challenge for the podium, with Johnstone finishing in eighth and Callister ninth.
The event served as an encouraging performance for both riders to give confidence for the remaining events in the season including the benchmark event in Sapporo later this month.
In the women's event, NSWIS athlete Emily Arthur finished in 18th place, missing out on the top-6 Women's Final.
In a dominating performance, 15-year-old teen sensation, Chloe Kim of the USA, became the first female to ever perform back to back 1080's and scoring a perfect "100" on her final run, taking out the victory.
IMAGE: Kent Callister & Nathan Johnstone boosting large out of the Park City halfpipe © Andrew Pattison