As the Australian Open comes to a close, the only thing more memorable than the matches is the courtside fashion seen on the likes of Rebel Wilson, Carrie Bickmore, Bec Hewitt, and a stylish set of "tennis girlfriends".

Costeen Hatzi is one of them, alongside the likes of Paige Lorenze, Hannah Dal Sasso, Nini Molnar and Morgan Riddle, and helped set the chic tone at this year's tournament.

But three years into her high-profile romance with tennis pro Nick Kyrgios, the 24-year-old still doesn't work with a stylist for events like the AO.

"I plan all my outfits myself, in advance," she reveals to 9honey Style, then laughs and adds, "I have a little folder on my phone called 'AO fits.'"

Hatzi, who was a normal uni graduate living in Sydney before she fell for Kyrgios, curates her courtside wardrobe by taking inspiration from the international 'It' girls who do it best, like Kendall Jenner and Hailey Bieber .

She studies their US Open and Wimbledon outfits, incorporating the elements she likes best into her own wardrobe as she prepares for the AO.

"Their style is very classic. They usually go for whites, the Ralph Lauren hat – I feel like that's iconic for tennis," Hatzi says.

Then she goes to work putting together outfits of her own that embody the same effortless, classy aesthetic while also working for the sweltering Australian heat.

AO fashion this year was all about clean lines and monochrome, which Hatzi elevated with trending pieces like a $90 pair of Billini heels, or luxury accessories like a set of Van Cleef and Arpels bracelets worth almost $20,000.

The 24-year-old is also intentional about promoting Australian brands while she's on home soil, stepping out in affordable local labels like Forever New, Witchery, and Viktoria and Woods over the course of the tournament.

Having grown up in Sydney before Kyrgios swept her off her feet and onto tennis courts all over the world, she's eager to use her platform to champion home-grown brands - and she's not alone.

Many of the international "tennis girlfriends" (her words) Hatzi rubbed shoulders with at the AO also embraced Australian fashion, like American influencer and entrepreneur Morgan Riddle

Riddle wore almost exclusively local labels like Benni, Arcina Ori and I Am Delilah, only appearing in one international brand during her tenure at the tournament.

It thrills Hatzi to see the partners of international tennis players diving into the Australian scene and sharing home-grown designers with their overseas audiences, though they do have to be careful about not wearing the same outfits.

"We just take our chances with that," Hatzi laughs, adding that they don't yet have a group chat where they coordinate who is wearing what.

With millions of social media followers between them, all eyes were on Hatzi and the other "tennis girlfriends" during the AO and for good reason.

She gained several thousand new Instagram followers over the course of the tournament and it's exciting to imagine what new fashion opportunities could come her way in the next 12 months.

Hatzi previously told 9honey can see herself launching her own fashion line in the future and this may well be a stepping stone on her path to a career in fashion.

"It's great to see Australian fashion and tennis tying into one another. I think it brings the two worlds together and gets more eyes on on the sport as well."

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