Minjee Lee put the Australian Open leaders on notice with a late birdie to claim early family bragging rights in the first round at Victoria Golf Club.
The Australian No.1 and world No.4 finished with a two-under-par 70, just missing an eagle chance at the par-4 18th when her approach shot landed six feet from the pin before her putt went awry.
She made no mistake earlier on the par-5 eighth, nailing an eagle with a long putt, while her round also included another birdie against two bogeys.
With the national championship a world-first mixed gender tournament, Lee's younger brother Min Woo Lee was three groups behind and finished level with the card on the men's par-70 layout.
The women's tournament favourite, Lee, who won this year's US Open, sits five shots behind round-one leader Grace Kim, who played her opening round at nearby Kingston Heath.
Kim teed off early on Thursday in benign conditions that helped deliver her birdie blitz while the wind picked up later in the day.
Lee felt she played well in the more difficult conditions.
"I hit it pretty solid, I just need to make a couple more putts to have that extra low one," the 26-year-old West Australian said.
"I drove it really well so I was in really quite prime position for my second shots but I found it a little bit tricky reading the greens.
"I haven't been out here that much, I only played the pro-am yesterday ... but I think as the week goes on, I think I'll get a little more knowledge on the greens and get more experience under my belt."
The top three women's scores, including fellow major winner Hannah Green (68), came at Kingston Heath which is generally considered the easier of the two courses.
But Lee felt there was still plenty on offer at Victoria which will host the final two rounds.
"It's playing a little shorter than Vic and all the par-5s are almost reachable for two," she said.
"So I thought there was going to be a little lower scores over at Kingston than here but there's quite a lot of opportunities here.
"You just have to play the par-5s well and have a birdie here and there on the par-4s.
"I missed a few on the back nine that I probably could have made and it would have really helped momentum but I'm two under and hopefully I can have a good score tomorrow."
