She answered with a birdie on the first hole, her second nine of the round, then ran off her birdie binge starting at the par-5 third and ending at the par-5 seventh.
Ko, who won her first LPGA tournament as a 15-year-old at the 2012 Canadian Open, said she still planned to stick by her goal of retiring from the sport at the age of 30.
After a start-stop affair so far in her rookie season on the LPGA Tour, Indian golfer Aditi Ashok, who jumped almost 20 spots on the priority list in the reshuffle done at the start of the month, is likely to get entry into more events leading up to the second Major next month end.
"A dream come true is all I can say!"
Second-ranked Korean So Yeon Ryn shot 70 while tournament defending champions Ariya Jutanugarn of Thailand managed 72.
Piller had six birdies and a bogey.
"I feel good about my game and I am looking forward to the week", said the soft-spoken youngster, who also played the Olympics a year ago. "You know, I kept in in play, which was nice". I would love to get my first win, but golf is merely my job.
Thompson, 22, certainly gave her pro-am partners a memorable experience on Wednesday with her surprise landing.
Ko is enduring the longest winless streak of her career, having gone 18 tournaments since her last win in July past year.
After a mixed start to the 2017 season, Ko went into the event under real threat of losing the No 1 ranking after 82 weeks at the top. She struck it very well and rolled a lot of great putts.
The LPGA star made the jump onto the course with retired Navy SEALs and a member of the Red Bull Air Force.
"Obviously, that's a really good start to the week", Ko said.
"I have been working on a lot of different aspects this year and my game feels good", Aditi told TOI on the eve of the $1.3m event. "Words can't describe the feeling".
A bogey at the sixth hole spoiled a round which featured five birdies.