Ashleigh Barty conceded she had simply been outplayed by Jennifer Brady. AFP/VNA Photo

BRISBANE — World number one Ashleigh Barty remains upbeat about her Australian Open preparations despite losing her opening match of the season at the Brisbane International on Thursday.

American qualifier Jennifer Brady notched up her first-ever win over a top-10 player when she beat Barty 6-4, 7-6 (7/4) at the Pat Rafter Arena.

It was Barty's first match on home soil since becoming world number one, played at the venue she trains at and in front of thousands of her adoring home fans.

Barty conceded afterwards she had simply been outplayed by Brady, who also beat former world number one Maria Sharapova in the first round.

"Jen was in control of the match -- she was in the centre of the court being the aggressor and I think you have to give credit where credit's due," said Barty, who practised with Brady early this week.

"She came through qualifying, but she's got a ranking that's kind of well below what a lot of people give her credit for.

"She's playing some exceptional tennis, so I certainly can't take that away from her. She played a great match today and deserved to win."

Barty grew up in Ipswich on Brisbane's western outskirts and has had hundreds of fans packing outside courts to watch her practice this week.

But when asked if she felt any pressure because of the attention, Barty insisted she didn't feel any different.

"I think that's (the pressure) all come you from you guys, if I'm being completely honest," she said.

"It doesn't change the way that I practice. It doesn't change the way that my team and I prepare. It doesn't change me as a person.

"I think that you guys enjoy the fact that you get something to write about and you have something to talk about. So hopefully I make it interesting for you, but I don't look at it beyond that."

Brady will now play two-time Wimbledon champion Petra Kvitova, who beat Russian qualifier Liudmila Samsonova 6-3, 6-2.

Karolina Pliskova, the world number two and defending champion, had to battle for two hours to avoid the same fate as Barty, eventually beating Australian wildcard Ajla Tomljanovic 6-4, 6-7 (5/7), 6-1.

Pliskova will meet Alison Riske of the United States in the quarter-finals.

Third seed Naomi Osaka was taken to three sets for the second match in a row before eventually overcoming the USA's Sofia Kenin.

Kenin won the first set in a tiebreak before Osaka took control, winning 6-7 (3/7), 6-3, 6-1.

Osaka will play sixth seed Kiki Bertens in the quarter-finals after the Dutchwoman beat Estonia's Anett Kontaveit 6-3, 2-6, 7-5. AFP