Defending champion Naomi Osaka was dumped out of the Australian Open third round on Friday by unseeded American Amanda Anisimova to open up the draw for title favourite Ashleigh Barty.

Anisimova, ranked 60th in the world, saved two match points to stun the former world number one 4-6, 6-3, 7-6 (10/5) and will now face Barty in the last 16.

It was a hugely disappointing end to Osaka's reign in Melbourne, having also gone out at the same stage at the US Open in September, after which she took a break from tennis.

"I'm speechless, I can't stop smiling," said the 20-year-old Anisimova.

Australia's Barty was a comfortable 6-2, 6-3 winner over Italian 30th seed Camila Giorgi, inching closer to a maiden Grand Slam crown on home soil.

"It was a pretty good performance," said Barty, 25, who is now 7-0 for the season and is yet to drop a set at Melbourne Park.

Also into round four is former two-time champion Victoria Azarenka.

The 24th seed crushed 15th seed Elina Svitolina as she tries to climb back to the top of women's tennis.

The 32-year-old Belarusian turned back the clock with a 6-0, 6-2 dismissal of her Ukrainian opponent and will now play French Open champion Barbora Krejcikova for a place in the quarter-finals.

"I think that's really what I'm trying to say is that ladder I want to climb step-by-step," said Azarenka, who won back-to-back Australian Opens in 2012 and 2013, of her efforts to get back among the elite.

"I think the danger for me is to try to skip a few steps. I think that is something I'm actually learning not to do. That's been helpful."

Krejcikova overcame a big fright against 2017 Roland Garros winner Jelena Ostapenko.

The Czech dropped the first set and was a break down in the second before coming through 2-6, 6-4, 6-4 and declaring her never-say-die attitude meant her rivals should now be afraid of her.

"I hope they are scared of me," said the 26-year-old, who was one of the standout players of 2021, winning three titles as she soared more than 50 places up the rankings.

Fifth seed Maria Sakkari and eighth seed Paula Badosa also went through.

Greece's Sakkari beat Veronika Kudermetova of Russia 6-4, 6-1 and Badosa came through 6-2, 5-7, 6-4 against Ukraine's Marta Kostyuk after bouncing back from a mid-match wobble.

On the men's side of the draw, world number three Alexander Zverev powered his way into the last 16 with a superb serving display against Moldova's Radu Albot.

The powerful German Tokyo Olympic gold medallist thundered down 16 aces and won 83 percent of his first serve points to put away the 124th-ranked Albot, 6-3, 6-4, 6-4.

Zverev will next take on Canada's 14th seed Denis Shapovalov.

Also through is Italian seventh seed Matteo Berrettini, who came through a five-set epic against talented Spanish 18-year-old Carlos Alcaraz 6-2, 7-6 (7/3), 4-6, 2-6, 7-6 (10/5).

Flamboyant French 17th seed Gael Monfils, who won the Adelaide warm-up event, continued his great early season form with a 7-6 (7/4), 6-1, 6-3 romp against 16th-seeded Christian Garin of Chile.

And Serbia's 77th-ranked Miomir Kecmanovic, who had been due to play – and probably lose – to world number one Novak Djokovic in the first round on Monday, now finds himself in the second week after knocking out Italian 25th seed Lorenzo Sonego 6-4, 6-7 (8/10), 6-2, 7-5.

Rafael Nadal is in action later Friday.

Nadal's path to become the first man to win 21 majors – he is tied on 20 with Roger Federer and Djokovic, who are both absent – could see him meet Zverev in the quarter-finals.