Australian Open 2019: Aryna Sabalenka beaten by teenager Amanda Anisimova

American 17-year-old Amanda Anisimova stunned 11th seed Aryna Sabalenka in straight sets to reach the last 16 at the Australian Open.

The youngest competitor left in the draw won 6-3 6-2 to become the first player born in the 2000s to reach the fourth round of a Grand Slam.

"This is an unreal feeling, I can't believe that this is happening right now," said the tournament debutant.

The world number 87 faces two-time Wimbledon champion Petra Kvitova next.

The Czech eighth seed, who won last week's Sydney International, beat Belinda Bencic of Switzerland 6-1 6-4 in 68 minutes.

"I'm feeling pretty good on the court physically and my mindset's good. I'm serving well too, which is important," said Kvitova.

Meanwhile, American Danielle Collins, who overcame 14th seed Julia Goerges in the opening round, moved into round four with a 6-3 6-2 win over France's 19th seed Caroline Garcia.

Next up for Collins will be 2016 champion and second seed Angelique Kerber, who thrashed Australian wildcard Kimberly Birrell 6-1 6-0 in 58 minutes.

Former world number one Kerber, on her 31st birthday, was far too good for the 20-year-old, who had caused a shock in the second round when she defeated 29th seed Donna Vekic of Croatia.

Anisimova's only other two Grand Slam appearances at the French and US Opens ended in first-round exits.

The youngster used her power to unleash 21 blistering winners and an accurate first serve on Belarusian Sabalenka, who had been among those fancied to challenge for the title in Melbourne.

"I was expecting a really tough match, she's a great player, so I really can't believe I got through this round," Anisimova said.

"I'm feeling really good out here, I played some great tennis."

She becomes the youngest American to reach a Grand Slam fourth round since Serena Williams at the French Open in 1998, and the youngest in Melbourne since Jennifer Capriati in 1993.

Fifth seed Sloane Stephens was made to work hard in her third-round victory over Croatian 31st seed Petra Martic.

The American 2017 US Open champion carved out just one break point - which she converted after having been broken herself in the first set - in a 7-6 (8-6) 7-6 (7-5) win.

She will face world number 44 Anastasia Pavlyuchenkova in the last 16 after the Russian's 6-0 6-3 victory over world number 31 Aliaksandra Sasnovich of Belarus.