Unheralded Casey Dellacqua held her nerve while French former world No.1 Amelie Mauresmo faltered as the Australian continued her giant-killing run at the Australian Open.

The 22-year-old West Australian moved into the fourth round of the tournament - where she will meet third-seeded Serb Jelena Jankovic - as well as taking the mantle as Australia's top-ranked female player.

It is heady territory for a player who had never won a match at the Australian Open in five attempts before this year, while Mauresmo's formidable record at Melbourne Park included the 2006 Open championship.

But, after a shaky start, Dellacqua showed great poise to hit out confidently in the final stages and win the third round encounter 3-6 6-4 6-4.

Mauresmo, who is trying to battle her way back to the top of the game, after an adductor injury last year caused her to topple to a six-year low in the rankings of No.18, threw in 10 double faults, including two in a row in the final game to give Dellacqua match point.

The Australian sealed victory with a confident forehand winner and said, after also coming from a set down in her previous two matches, she knew she could handle the pressure of a tight finish.

"I knew that (Mauresmo) was struggling (with the pressure), I thought she was struggling a little bit," Dellacqua said.

"I know the last match and the match before that, when it comes to the crunch, I've had a lot of confidence ... I think maybe that's what helped me through."

Dellacqua, who has now beaten two players inside the world top 20 in succession, having downed 15th seeded Swiss player Patty Schnyder in the second round, said a huge Rod Laver Arena crowd also helped carry her through.

"I could feel the whole crowd, I could feel Rod Laver almost vibrating because the crowd was so loud, it was just awesome," she said.

She was particularly inspired as she returned from the final change of ends.

"It was just like the whole crowd was behind me, all I wanted to do was win ... you never have that feeling anywhere else in the world," she said.

Dellacqua, who only broke into the world top 100 for the first time last August and is now on the cusp of the top 50, is the only Australian remaining in the women's singles draw.

But, while admitting her performances in Melbourne had raised her sights about what she could achieve, she said they would not cause her to change her aggressive approach when she comes up against Jankovic.

"For me now I've still got nothing to lose, I'm in a great position," Dellacqua said.

"I've played Jelena in Bali last year. I've played her before so I know a bit about her game and I've obviously seen a lot of her play.

"So you know what I'm just going to go out and have fun, enjoy the crowd, it's so amazing out here, and just go for it."

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