On a night when the oldest player left in the main draw made a shock exit while continuing to chase history, the youngest player turned in a sparkling performance to make a little history of her own.

 

Fifteen-year-old Coco Gauff (pictured above) defeated reigning Australian Open champion Naomi Osaka, 6-3, 6-4, on Day 5 in Melbourne in a rematch of their US Open clash last summer, becoming the youngest player to dethrone a defending champion at the tournament in the Open era.

 

"I feel like even before the tournament, I think almost every player has a belief that they can win it," Gauff said.

 

"Some stronger than others. So I don't even think about the defending champion and all this because, in the moment, I'm just thinking about playing the ball. I just always have the belief I can win, regardless of my opponents. ADVERTISEMENT Obviously, today was a huge boost in confidence."

 

Gauff broke Osaka at 3-4 in the first set, then twice more in the second, as she put the lessons she learned from her Flushing Meadows loss to good use. She handled Osaka's pace much better and didn't seem as daunted by the occasion. Osaka credited her with serving better than she did in New York, and she said it felt like Gauff was being more aggressive while playing with finer margins. 

 

The teen was one of four Americans to advance to the Round of 16, joining Alison Riske, who rallied to beat Julia Goerges of Germany, 1-6, 7-6, 6-2; Sofia Kenin, who defeated Shuai Zhang of China, 7-5, 7-6; and Tennys Sandgren, who toppled fellow American Sam Querrey, 6-4, 6-4, 6-4.

 

Gauff will play Kenin for a spot in the quarterfinals, with the winner set to play either Qiang Wang of China or Ons Jabeur of Tunisia. Riske will face world No. 1 Ash Barty for the right to advance to the final eight. Sandgren gets No. 12 seed Fabio Fognini on Sunday and could play No. 3 seed Roger Federer in the quarters.

 

But while the talented teen progressed to the fourth round of a Grand Slam for the second time in three major appearances, 23-time Grand Slam singles winner Serena Williams, who turns 39 in September, made her earliest Aussie Open exit in 14 years, losing a three-set thriller with Wang, 6-4, 6-7, 7-5.

 

If Williams’ exit was the top story of Day 5, Gauff’s historic win wasn’t far behind.

 

She became the youngest player to beat a defending champion at any Grand Slam since another American, Jennifer Capriati, beat Gabriela Sabatini in the 1991 US Open quarterfinals at 15 years, 163 days old. Gauff is also the youngest player to beat a Top 5-ranked opponent since that same Capriati win in New York almost three decades ago.

 

Gauff, the third player in the last 30 years to earn at least eight Grand Slam match wins before her 16th birthday, is the youngest player to reach the last 16 at the Australian Open since Martina Hingis reached the quarterfinals in 1996.

 

Should Gauff reach the quarters, she would become the youngest player to go that deep in a major since Sesil Karatantcheva reached the quarters at Roland Garros in 2005 and the eighth player to make the final eight at a Slam—in a 128-player draw—before their 16th birthday. After her victory over Osaka, Gauff told reporters the win was one of the best of her career.

 

"I don't really have a ranking list for that, but definitely it has to be somewhere around the top," she said. "I thought I played really well today, and I was pretty composed and really calm."

 

By contrast, Williams, who was trying to match Margaret Court's all-time record of 24 Grand Slam women's singles titles, said she didn't play to her ability against Wang, a player to whom she dropped just one game in a 45-minute thrashing at the US Open in September.

 

"I mean, personally, I made a lot of errors," Williams said. "I didn't hit any of those shots in New York or, in general, in a really long time. So that's good news. I just made far too many errors to be a professional athlete today.

 

"She served well. I didn't return like Serena. Honestly, if we were just honest with ourselves, it's all on my shoulders. I lost that match. So it is what it is. Like I said, it's not about the tournament; it's just like I can't play like that. Like, I literally can't do that again. That's unprofessional. It's not cool."

 

Elsewhere on Day 5, No. 10 seed Madison Keys lost to No. 22 seed Maria Sakkari of Greece, 6-4, 6-4, and Tommy Paul fell to Marton Fucsovics of Hungary, 6-1, 6-1, 6-4.  

 

Three Americans are in singles action on Saturday, with No. 19 seed John Isner facing former Australian Open champion and No. 15 seed Stan Wawrinka of Switzerland, No. 29 seed Taylor Fritz playing fifth-seeded Dominic Thiem of Austria, and CiCi Bellis battling No. 16 seed Elise Mertens of Belgium.

 

Doubles action continues in second-round play, and the boys’ and girls’ junior competitions get underway.