McIntosh made her move in the closing stages but Pallister responded to touch the wall first in one minute, 53.67 seconds, 0.19 ahead of the Canadian.
New Zealand's Erika Fairweather was third.
"Racing this week at Pan Pac is the first taste of racing at the Olympics in two years' time," Pallister said poolside at the meet.
"I don't often race the 200 individually, so going 1:53 is wicked here."
The 24-year-old won Olympic gold as part of Australia's 4x200m freestyle relay team at the Paris Games in 2024.
She also claimed silver in the 800 at last year's World Championships in Singapore, finishing behind American Katie Ledecky and ahead of McIntosh.
