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 Petra Kvitova or Belinda Bencic next.

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.