Coco Gauff greets Japan's Naomi Osaka at the end of their women's singles match on day five of the Australian Open tennis tournament in Melbourne on Friday. AFP
The American, the youngest player in the draw and making her Melbourne debut this year, defeated the third seed 6-3, 6-4 to avenge a heavy defeat at last year's US Open.
Gauff plays compatriot and 14th seed Sofia Kenin or China's Zhang Shuai in the fourth round after a comprehensive victory, which underlines her rare talent.
This was the second instalment of a budding rivalry between Gauff and Osaka that could light up tennis for the next decade, having met at the US Open, where the 22-year-old Japanese won easily.
On that occasion it was the teenager who struggled with nerves, but the tables were turned this time.
Even so, the scale of the achievement had not fully set in for Gauff, the youngest woman to beat a top-five opponent since Jennifer Capriati defeated Gabriela Sabatini at the US Open in 1991.
"On the court I was definitely, what is my life? All these people clapping for me," she said.
"I'm still new to this, but I'm sure I'm not used to it." She was in such shock afterwards that "I don't even remember what I did, but I think I was more in disbelief so I didn't really know what to do." "I'm trying to think of what even happened today."
The sense of bewilderment took on a whole new level when Roger Federer became one of the first people to congratulate her.
"I was, like, 'Thank you,' trying to be calm. Inside, I was, like, Oh, wow!"
Gauff, who spent time training with Serena Williams in the off-season, had said she would be less nervous and more aggressive this time round in facing the world number four Osaka.
And so it proved as they rattled through the first five games in barely 15 minutes at the 15,000-capacity Rod Laver Arena.
Osaka fired into the net to drop serve in game eight and then racked up more unforced errors in gifting Gauff the first set in 32 minutes.
"Come on!" shouted Gauff, ranked 67 but fast making a name for herself as the most exciting prospect in women's tennis.
The young American carried the momentum into the first game of the second set, breaking a subdued and rattled Osaka, a two-time Grand Slam champion.
The Japanese broke back for 1-1 when Gauff volleyed into the net, but it was a rare mistake by the American and she broke once more, before serving for the match at 5-4.
The nerveless teenager clinched victory on the first match point when Osaka fired into the net.
Gauff announced herself to the sporting world at Wimbledon last year when, as a qualifier, she stunned Venus Williams in the first round.
She did the same thing to the seven-time Grand Slam champion on her Melbourne debut this week, then came back from a set and 3-0 down to defeat Sorana Cirstea on Wednesday.
When Gauff and Osaka met five months ago in New York, also in round three, then-world number one Osaka crushed the tearful and overawed teenager 6-3, 6-0 in a little over an hour.
"I learned a lot from that US Open. Not even just playing against Naomi, but the whole tournament," said Gauff.
"I think I was on edge and I had the three-setters in the first two rounds of the US Open, and I think that was just dealing with all of the media.
"I feel like now I'm more playing, just having fun.
"And winning is a cherry on top."
Serena Williams crashed out, 15-year-old Coco Gauff stunned Naomi Osaka and Roger Federer survived a five-set thriller as the form book went flying out of the window
Fifteen-year-old prodigy Coco Gauff set up an Australian Open blockbuster with defending champion Naomi Osaka on Wednesday, as a pumped-up Serena Williams
With her 38th birthday fast approaching, the clock is ticking for Serena Williams and on her pursuit of a record-equalling 24th Grand Slam title at Roland Garros. The American star won her most recent major at the Australian Open in 2017 while pregnant.
The season-ending Dubai double-header begins on Wednesday as the Fire course at Jumeirah Golf Estates is all set to welcome European Tour’s finest players for the inaugural Golf in Dubai Championship presented by DP World.
The UAE, who are Associate Members of the ICC, have already played two 50-over World Cups in 1996 and 2015. The thirteenth edition of the showpiece event will be held in India in 2023.
The council said, “Coinciding with the celebrations of UAE National Day, we recall the participation of the late Argentine football legend, Diego Maradona, in previous Dubai Sports Council National Day celebrations.”