Thrillers in sport are like buses: you wait ages for one and then three come along at once.

The fifth day of the Australian Open saw 15-year-old Coco Gauff re-emerge and stun defending champion Naomi Osaka in a brutal display in Melbourne.

That came just after pre-tournament favourite Serena Williams, chasing a record-equalling 24th Grand Slam singles title, was knocked out by Wang Qiang.

And then Roger Federer capped the day by somehow coming through a five-set thriller against John Millman.

That's all without mentioning Caroline Wozniacki bringing an end to her sterling 15-year career.

Oh, and defending Novak Djokovic breezed into the fourth round too...

'What is my life?'

When Gauff was born in 2004, Venus Williams had won four of her seven Grand Slams.

Two years ago, Gauff lost in the first round in the Australian Open juniors. Even last year, when Osaka was lifting her second Slam trophy in Melbourne, Gauff was just 14 and ranked 684th in the world.

At 11pm on the night before her final qualifying match for Wimbledon 2019, Gauff stayed up to take a science test. The next morning, she took just under an hour to reach the main draw.

Wimbledon was her breakthrough; she stunned Venus in the first round and marched through to the last 16, where she lost to eventual champion Simona Halep.

Not every Slam performance has gone the teenager's way - she was thrashed by Osaka at the US Open last year, with both players crying after Osaka's 6-3 6-0 win.

October saw Gauff win her maiden WTA title. She spent the off-season practising with Serena Williams, whose posters she had on her wall. Former First Lady Michelle Obama asked for her autograph.

And then, on the fifth day in Melbourne, Gauff produced a mature, hard-hitting performance to end Osaka's title defence in straight sets on the Rod Laver Arena.

She admitted afterwards that while she had passed him in a corridor, she had yet to meet the Arena's legendary namesake - and she wants a selfie for her Instagram.

"Oh my gosh. This is crazy," Gauff said after her win over Osaka. "I don't know where that came from. Honestly, like, what is my life?"

And Gauff's reward for reaching the last 16 of a Slam?

"I'll probably do homework tomorrow," she said.

"My teachers are giving me some time because of the circumstances... they're letting me submit some assignments late, so that's nice."

'What she's doing is nuts' - reaction to Gauff win

Former world number five Daniela Hantuchova on BBC Radio 5 Live: "Coco just makes it look so natural. It's why she's going to be one of the greatest - if not the greatest - of all time."

Tennis journalist Ben Rothenberg: "What Coco Gauff is doing is nuts. It's pretty hard to overstate that."

TV presenter Richard Osman: "If Coco Gauff wins two Grand Slams a year until she's Serena's age - which you wouldn't bet against - she'll win 46."

Serena Williams, a 23-time Grand Slam winner: "I was nowhere near Coco's level either on the court or off the court, not even close. I was nowhere near as smart and eloquent as she is. It's nice to see."

Federer fights demons in marathon win

When he was 8-4 down in the final set tie-break, Federer admitted he was getting ready to "explain myself in the press".

He had lost his past three five-set Slam matches - including that epic Wimbledon final against Novak Djokovic last year - and it was Millman who stunned him at the US Open in 2018.

But, after losing the first set, after serving five double faults and hitting 82 unforced errors, Federer somehow rallied to win the final six points of the match and claim victory in four hours three minutes.

"The demons - they're always there, they're lurking," Federer said after his win.

"I can't even speak any more. It came down to the wire."

However the victory came, Federer is still in with a chance of claiming a seventh Australian Open trophy and a record-extending 21st Grand Slam title.

'Unprofessional' Serena bows out

It was a different story for Serena Williams, who suffered her earliest exist in at the Australian Open since 2006 at the hands of Chinese 27th seed Wang.

Wang won just 15 points when the two last met at the US Open, but she dialled in to beat Williams 6-4 6-7 (2-7) 7-5 and reach the fourth round.

Williams has reached four Grand Slam finals since returning from maternity leave and has lost all four in straight sets.

She may be in her 23rd year as a professional but she says she still has the drive to equal Margaret Court's all-time record.

"I don't play just to have fun. To lose is really not fun," she said.

"I just made far too many errors to be a professional athlete today."

Wozniacki says goodbye & Tsitsipas is knocked out

Williams was comforted in the locker room afterwards by her long-time friend Wozniacki, who retired after her third-round defeat by Ons Jabeur.

The crowd serenaded the Dane - a champion in Melbourne in 2018 - with 'Sweet Caroline' as she did a lap of honour.

Wozniacki announced in November that the Australian Open would be her last tournament.

Meanwhile, Greek Stefanos Tsitsipas added to the shocks when he fell in straight sets to former Wimbledon finalist Milos Raonic of Canada.

Tsitsipas, who won the year-end ATP Tour finals in 2019 and beat Federer last year in Melbourne, said some of Raonic's shots were like "getting punched in the face".

"I felt a bit stupid returning his serves. It's a strange game of tennis in general," he added.

"It's one shot that you can get knocked down all the time, and you're just there, getting punched in the face with one shot.