America's Coco Gauff has caused one of the biggest upsets of the tournament by knocking out defending champion Naomi Osaka in straight sets in the Australian Open.

The 15-year-old rising star beat the third seed 6-3 6-4 in one hour seven minutes in front of a packed crowd at the Rod Laver Arena in Melbourne.

She showed no signs of nerves after closing out the first set and immediately broke the Japanese player in the first game of the second. From there she held her nerve and took advantage of some error-strewn play from the defending champion.

Gauff, who was beaten by Osaka in last year's tournament, will now go on to play either China's Zhang Shaui or American Sofia Kenin in the fourth round.

The young star had already overcome her hero, Venus Williams, in the first round and is showing maturity and cementing her name as a star of the future.

After the game she was visibly emotional, saying: "Honestly, what is my life? Like, oh my gosh. Two years ago I lost first round in juniors and now I’m here. 

"This is crazy! I mean, I love it down here. Oh my gosh. Like, honestly? Thank you guys so much from the bottom of my heart. Like, oh my gosh, I’m on Rod Laver Arena. I can’t believe this!"

She then joked about having to go back and do her school work adding: "My teachers, they’re giving me some time because considering the circumstances they’re letting me submit some assignments later."