Playing alongside seven-time major winner Karrie Webb and another major champ and former world No.1, Jiyai Shin from South Korea, the 20-year-old Porter claimed the honours with a bogey-free six-under 66.
It left her atop the leaderboard with Thailand's Pavarisa Yoktuan.
Shin was in a group of five tied for third at five-under, while Webb hung tough and birdied the 18th to get back to par.
But the story of the day was Porter.
Playing on the more difficult Beach course in the trickier afternoon conditions after the wind got up, she was off to a flying start with two birdies and an eagle inside the opening five holes.
There were two more birdies at the 10th and 13th and a clutch par-saving effort on the final hole of the day - all of it with a big smile on her face.
"I had so much fun out there," said Porter.
"With two former world No.1s and major champions - what a group.
"I was pumped last night and it was really nice to come out and put a score on the board.
"I had nerves all day if I'm being honest.
"I was definitely on edge the whole time, but it kind of worked for me and I used it to my advantage and kept on top of everything."
Porter, who turned professional in December 2021 and will play on the secondary Epson Tour in the US this year, is one of many young Australian female golfers to have benefited from the mentorship of Webb.
"Karrie and Jiyai are amazing to play with," she said.
"You pick their brains about things every now and then.
"I tried not to today, but it's hard not to when you've got two amazing players with you."
Grace Kim, Sarah Jane Smith, Kristalle Blum and amateur Sarah Hammett were the next best-placed Australians in a tie for eighth at four under.
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