San Francisco Frontiers - Extreme heat triggers Melbourne match suspensions as Sinner battles on

Players and spectators roasted on day seven at Melbourne Park, where temperatures were forecast to soar to 40C.

The tournament has a Heat Stress Scale of 1-5, with five the highest.

It hit five in the early afternoon, when it was about 36C, prompting the suspension.

The third-round meeting between Sinner and the American Eliot Spizzirri at Rod Laver Arena stopped for about 10 minutes, allowing time for the roof to close.

It helped save Sinner, who was suffering from cramp and wilting in the heat.

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 either American ninth seed Taylor Fritz or the Swiss veteran Stan Wawrinka next.

The 40-year-old Wawrinka must try and rouse himself on his Australian Open farewell after a sapping five-set win in round two.

Matches on outside courts remained suspended in the late afternoon, but organisers hoped they could get going again in the early evening.

The three courts with roofs resumed after a short delay to close them.

- 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 well used to baking 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 in 66 minutes.

"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.

Multiple major winners Iga Swiatek and Naomi Osaka also both feature on day seven at Melbourne Park.

- 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."

Last up on centre court is two-time Melbourne Park champion Osaka, who wowed the crowds earlier this week when she emerged for her opening match in a jellyfish-themed outfit.

On court she has not been so dazzling and faces home hope Maddison Inglis, a qualifier.

The winner goes up against either six-time Grand Slam champion Swiatek or 31st-seeded Russian Anna Kalinskaya.

Swiatek is aiming to complete the career Grand Slam of all four majors, with Australia the only one missing from her CV.

K.Hernandez--SFF