Marta Kostyuk, 15, extends her dream Melbourne run

Teenager Marta Kostyuk already knows how she will spend more than 140,000 Australian dollars in prize money after reaching the third round in Melbourne.

The 15-year-old from Ukraine beat local Olivia Rogowska 6-3 7-5 in the Australian Open second round on Wednesday.

The winner of the junior title last year, Kostyuk will take home 142,500 AUD if she loses to countrywoman Elina Svitolina next.

Kostyuk, who had won just over 6,000 AUD heading into the year's first major, said she had some idea where her money would be spent.

"I already know a little bit where I'm going to spend this, but I didn't really think, because, like some big investment or something," she said.

"Now I'm still keeping money. It's like I got it and I go and spend.

"Maybe I will get the presents for my family, first of all, of course. Because I have big family. And then for myself a bit."

Kostyuk became the first 15-year-old since Nicole Vaidisova in 2005 to make the third round of a grand slam.

The messages were already flowing to Kostyuk after her run continued at Melbourne Park.

"I take the phone, and I had to eat at the same time. My mum told me leave the phone and eat properly. Because I didn't have normal breakfast, that's why I felt quite bad today on court," she said.

"And I was quite hungry and at the same time I had to check.

"Once I enter WhatsApp, I had to put the phone, and I think, no, I didn't still reply to a lot of people."