Volkswacht Bodensee - Heat triggers Melbourne chaos as Osaka out, Sinner survives

Players and spectators roasted on day seven at Melbourne Park, where temperatures soared to 38C.

The tournament's Heat Stress Scale hit the highest level of five in the early afternoon, prompting the suspension on courts without roofs and play did not resume until after 7:00 pm.

On a dramatic day on and off court, two-time champion Osaka was supposed to be in action in the third round but pulled out hours before because of an abdominal injury.

The Japanese star, who made a grand entrance this week in a jellyfish-inspired outfit, wrote on Instagram that "it breaks my heart".

She was due to face Australian qualifier Maddison Inglis, who goes on to play Iga Swiatek in the last 16.

Swiatek, the second seed from Poland, survived a roller coaster to beat 31st Russian seed Anna Kalinskaya 6-1, 1-6, 6-1.

- Roof saves Sinner -

Reigning champion Sinner admitted he was saved by the roof in his meeting with the American Eliot Spizzirri at Rod Laver Arena.

Play was stopped for about 10 minutes because of the baking heat, allowing time for the roof to close.

Sinner had been suffering from cramp in the fierce sun.

But with the roof shut he pulled through 4-6, 6-3, 6-4, 6-4 over a gruelling 3hr 45min.

"I struggled physically a bit today as you saw. I got lucky with the heat rule, they closed the roof," said the second seed.

His reward is a clash next with fellow Italian Luciano Darderi, the 22nd seed who defeated Russia's Karen Khachanov in four sets.

On a historic day for Italy, fifth seed Lorenzo Musetti saw off Tomas Machac in five sets.

It was the first time that three Italian men had reached the last 16 of the Australian Open.

Musetti goes up against American ninth seed Taylor Fritz after he ended the run of Stan Wawrinka on the popular Swiss veteran's farewell to the tournament in four sets.

The 40-year-old former champion is playing his last season.

- Keys impresses -

Earlier, women's defending champion Madison Keys revelled in the scorching temperatures to set up a last-16 showdown with podcast co-host Jessica Pegula.

Matches started an hour earlier than usual because of the heatwave, and Keys had no intention of hanging about.

She dismissed former world number one Karolina Pliskova of the Czech Republic 6-3, 6-3 in a statement victory.

After admitting to being nervous and timid in embarking on her title defence, this was more like the Keys that stunned Aryna Sabalenka in the final a year ago.

The 30-year-old Keys said that being based in Florida meant she was used to hot temperatures.

"I am feeling really good and I was excited for the heat today, and ready for it," she said.

The ninth seed faces good friend and compatriot Pegula for a place in the quarter-finals.

The sixth-seeded Pegula powered past unseeded Russian Oksana Selekhmeteva 6-3, 6-2.

"Nice to be first out on court and not a super long match and didn't need to kill myself in the heat today," she said.

Pegula and Keys know each other well, even hosting a tennis podcast together.

Another title contender, Amanda Anisimova, made light work of fellow American Peyton Stearns 6-1, 6-4.

- Confident Djokovic -

Serbian great Novak Djokovic faces 75th-ranked Dutchman Botic Van de Zandschulp in the evening prime time slot on Rod Laver Arena.

The 38-year-old former world number one has looked in imperious form so far, yet to drop a set and striking a confident tone.

Djokovic, who has been scaling back the number of matches he plays to wring the most out of his ageing body, said: "It's all been positive so far, positive signs."

C.Koch--VB