Naomi Osaka defeated by Amanda Anisimova at Australian Open, Ash Barty through to fourth round

Ash Barty has reached the fourth round of the Australian Open, but defending champion Naomi Osaka has been knocked out of the tournament by unseeded American Amanda Anisimova.

Barty progressed with a 6-2, 6-3 win over Italian 30th seed Camila Giorgi on Rod Laver Arena, with most observers feeling it was a mere formailty Osaka would be her opponent in the last 16.

But instead, it will be Anisimova, who scored a stunning upset victory over the four-time major winner, claiming a 4-6, 6-3, 7-6 (10-5) triumph on Margaret Court Arena.

Osaka had two match points when she led 5-4 in the third set, with the 60th-ranked Anisimova serving to stay in the contest.

Anisimova held serve before a super tiebreak was later needed to decide the match. The 20-year-old forced 13th-seeded Osaka to play catch-up early, always keeping her nose in front on the scoreboard.

She served for the match at 9-5, with an ace sealing the result and leaving the former world number one's title defence in tatters.

«I thought she [Anisimova] played really well,» Osaka said after the match.

«For me, I thought it was a pretty high-level match. I think the pace of her ball surprised me, but other than that, it was fun to play.»

Anisimova — who had never played Osaka before Friday night — entered the tournament on the back of a WTA Tour event victory at Melbourne Park.

She said she was determined not to get carried away with her win, especially with Barty now her next opponent.

«I'm just enjoying one match at a time right now,» said Anisimova, who recently included renowned Australian coach Darren Cahill in her support team.

«I don't think that I played amazing tennis today. I think it was a little bit tough, and I was pretty nervous.

»Hopefully I can build on this into the