MELBOURNE, Australia — Marta Kostyuk was such a perfectionist when she started playing tennis as a child, she'd blow up in anger if she missed even a single ball. It made tennis completely unenjoyable.

"I always want to win, no matter what," the Ukrainian teenager said. "If I was losing, it was a tragedy. It was, like, I don't want to play anymore."

Now, after beating Olivia Rogowska 6-3, 7-5 on Wednesday to become the youngest player to reach the Australian Open third round in two decades, Kostyuk is finding peace with the ups and downs of the sport. All at the wise old age of 15.

"Now, I start to enjoy it," she said. "Finally."

Kostyuk's performance in Melbourne is remarkable considering just how far she's come in such a short time. The Australian Open is not only her first Grand Slam, but her first main draw at any WTA-level tournament.

Her ranking? No. 521. Career earnings? Less than $7,000.

Yet the bubbly Kostyuk's game looks more than ready for this moment. Granted a wild card to the qualifying draw after capturing the Australian Open junior title last year, Kostyuk won three matches to earn a spot in the main draw, then upset the No. 25-seeded Chinese veteran Peng Shuai in the first round.

Perhaps an even tougher challenge, she followed that up with a convincing win over Australian wild-card entry Rogowska in front of a partisan crowd at Margaret Court Arena, the No. 2 show court at Melbourne Park.

The stats weren't pretty — 45 unforced errors to just 22 winners — but Kostyuk handled the pressure well. A power player who hits big off both sides, she kept going for her shots even when she misfired.

And misfire she did aplenty. While serving for the match, she clubbed a ball off the frame of her racket that nearly hit a spectator in the crowd. (Kostyuk blamed serving into the sun: "You throw the ball and you hit the sun, actually.")

Kostyuk was an acrobat growing up and was so talented, she placed fourth in the Ukrainian national championships — as a child. But she wanted to spend more time with her mother Talina Beiko, a former pro tennis player and now coach, so she gave up acrobatics to focus on tennis at 11.

Since winning the Australian Open girls title last year, she's made the jump to the pro level. She's represented by a high-profile manager, former world No. 3 Ivan Ljubicic, who currently coaches Roger Federer. The impact on her game has been immediate.

"Ivan is always helping me when he sees me," she said. "And Roger, we speak twice. You know, really, like speak. Not like, 'Hey, how are you.' That was nice."

With her run in Melbourne, Kostyuk has become the youngest player to reach the third round since Martina Hingis made the quarterfinals at 15 in 1996.

This has already brought her a great deal of attention — the kind that has proved difficult for other young players in the past. Part of the reason breakthroughs like Hingis' are so rare these days is that the WTA Tour has limited the number of tournaments teenagers can play. Kostyuk is only eligible for 10 tournaments at age 15.

Even so, young players are still "hyped a lot," said one-time Swiss prodigy Belinda Bencic, who was a U.S. Open quarterfinalist at 17.

"When you win one, two matches, everybody focuses on you," said Bencic, who has since struggled with injuries and lost her second-round match at the Australian Open only two days after an upset win over Venus Williams. "Suddenly, you're the one who has to win, which actually shouldn't be like that."

Bencic hopes Kostyuk "keeps enjoying all of this and remembers the feeling how it is when you're excited first time, first Grand Slam, and to keep it this way."

Kostyuk's next opponent will be a much tougher test — Ukrainian Elina Svitolina, who is seeded fourth. Svitolina has been dealing with what she called "injury issues" and wasn't sure if she'd be fit enough to play in Melbourne. Still, she goes into the match the heavy favorite.

"She has nothing to lose, so that's why I know she goes just for everything," Svitolina said of her younger countrywoman. "A little bit like headless chicken."

Kostyuk gives herself a chance, however. She believes she's playing better and better with each match.

"I will just enjoy it," she said. "I will just try to show my best tennis."