The four-time Grand Slam champion from Japan won 6-4, 6-2 in another confidence boost ahead of the Australian Open starting on January 12 in Melbourne.
Osaka was contesting her first semi-final since 2022, having taken a break from tennis and becoming a mother in 2023. She returned to the sport a year ago.
The 27-year-old showed no sign of the nerves that had marked her first three wins in Auckland, producing a clinical performance to set up a final on Sunday against Clara Tauson of Denmark.
"Of course I'm really happy to get to the final here, I've actually never got to a final a week before Melbourne so this is like a career first for me," said Osaka, a two-time Australian Open champion now ranked 57th.
"In my head I'm really happy. But there's always constantly things to improve to get better, no matter how old you are."
Osaka's power and precision proved too much for the 78th-ranked Parks.
The American faded in what was her second match of the day, having had her quarter-final pushed back by rain on Friday.
Osaka's four wins this week have come against opponents ranked below her at a tournament lacking a strong field.
That will change in the final against 50th-ranked Tauson, who beat unseeded American Robin Montgomery 6-4, 6-3 in the other semi-final.
Earlier in the day, Tauson toppled American top seed Madison Keys 6-4, 7-6 (9/7) in a quarter-final that was interrupted by rain on Friday night.
