The 23-year-old second year professional from Perth fired seven birdies and one bogey on the tight and tree-lined Perugia Golf Course to end a stroke clear of England's Rebecca Hudson, with a group of six further players on three-under-par.
Hillier felt right at home on the course, which reminded her of Cessnock Golf Club in Sydney, playing in temperatures of 28C. "I felt right in my element today because Perth's nice and hot and today was perfect out there. We've been very lucky with the weather," said Hillier, who recorded a career best finish of third in Slovakia 12 months ago.
"It was a great start. I've just changed coach and changed my swing a little bit. I felt really good out there. I didn't put any pressure on myself and free flowed and it was good fun."
The Joondalup Golf Club player began with three birdies on the back nine, at holes 14, 16 and 17 before dropping her only shot of the day on 18. She then picked up four birdies on the front nine, including a chip in from the bunker short of the green on her penultimate hole.
She added: "I chipped in from the bunker on eight. I wasn't too worried about that because I love those little flop shots. A minute before I said, "˜I'm going to hole it,' and I did. I kept it pretty solid all day. 15 greens and 27 putts. It felt really good and consistent today so the hard work is paying off."
Hudson, a four-time winner on the Ladies European Tour, played earlier in the day and began with six pars but picked up her first stroke at the par 3 seventh. She then birdied 10, 11, 14 and 16.
"I played very well, had the ball under control and there are some holes out there which you can attack and I did and I played sensibly when I needed to," said Hudson, who won three tournaments in 2008.
"I'm very pleased as I had no bogeys. I played sensible and I think the US Open last week taught me a lesson in playing sensible. There are some good attacking holes out here so I took my chances and when I needed to be sensible I was. The 18th green, I think I only missed two greens in regulation, I had to run up the bank and it was very "˜a la Pinehurst' so it was good and I learned a lot last week which I've brought forward this week."
Those on three-under were Italian Diana Luna, England's Holly Clyburn and Floerntyna Parker, Amy Boulden of Wales, Germany's Ann-Kathrin Lindner and Danish rookie Nicole Broch Larsen.
Luna enjoyed playing for a home gallery and after her round of 69, she said: "It was a very solid start. I'm pleased with the way I've been playing today and looking forward to a nice weekend."
Boulden made a poor start with a double bogey on the first and a bogey on four but recovered with seven birdies. She said: "I feel a lot more confident coming into this week and I played well in the practice round yesterday, which gave me a lot of confidence. I couldn't hit a fade last week and this week I'm managing to hit that with my irons."
Leading scores at the end of Round 1:
66 - Whitney Hillier (AUS)
67 - Rebecca Hudson (ENG)
69 - Florentyna Parker (ENG) , Amy Boulden (WAL) , Nicole Broch Larsen (DEN) , Holly Clyburn (ENG) , Diana Luna (ITA) , Ann-Kathrin Lindner (GER)
70 - Cassandra Kirkland (FRA) , Celine Herbin (FRA) , Beth Allen (USA) , Stacy Lee Bregman (RSA) , Krista Bakker (FIN)
71 - Lucy Williams (ENG) , Leigh Whittaker (GER) , Sophie Walker (ENG) , Mallory Fraiche (USA) , Kelsey Macdonald (SCO)
72 - Sophie Gustafson (SWE) , Pamela Pretswell (SCO) , Caroline Martens (NOR) , Noora Tamminen (FIN) , Maria Salinas (PER) , Marianne Skarpnord (NOR) , Julie Greciet (FRA) , Heather Macrae (SCO)
73 - Karolin Lampert (GER) , Veronica Zorzi (ITA) , Daniela Holmqvist (SWE) , Titiya Plucksataporn (THA) , Vittoria Valvassori (ITA) , Isabell Gabsa (GER) , Georgina Simpson (ENG) , Connie Chen (RSA) , Louise Larsson (SWE) , Linda Wessberg (SWE) , Bree Arthur (AUS) , Caroline Afonso (FRA) , Jade Schaeffer (FRA) , Henni Zuel (ENG) , Paula Hurtado (COL) , Elina Nummenpaa (FIN) , Chloe Leurquin (BEL)
74 - Steffi Kirchmayr (GER) , Julie Tvede (DEN) , Mia Piccio (PHL) , Nikki Garrett (AUS) , Mireia Prat (ESP) , Holly Aitchison (ENG) , Ursula Wikstrom (FIN) , Jessica Ji (KOR) , Nontaya Srisawang (THA) , Sophie Sandolo (ITA) , Virginia Elena Carta (ITA) , Patricia Beliard (FRA) , Felicity Johnson (ENG) , Louise Stahle (SWE) , Sandra Carlborg (SWE) , Cathryn Bristow (NZL)