Extreme temperatures triggered the Australian Open’s heat protocols on Saturday, wreaking havoc on the day’s schedule and forcing fans to go without tennis on the outside courts for much of the afternoon.

The defending champion, Jannik Sinner, was one of the beneficiaries of the heat protocols being implemented, the Italian struggling with cramps and down a break in the third set against American world No 85 Eliot Spizzirri.

Sinner recovered to win in four sets despite the earlier drama, as Melbourne temperatures climbed towards 40C in the afternoon and play was suspended on outer courts until 5.30pm at the earliest.

The Australian Open’s heat stress scale triggered a suspension at about 2.30pm, just as Sinner was beginning to severely cramp during his third round match against Spizzirri. Play on the outside courts was paused, and arena roofs were closed. When the players returned to centre court after a break of about 10 minutes, Sinner immediately broke back and looked far more like the athlete that has won the past two men’s singles titles at Melbourne Park.

The Australian Open issued a statement on social media at 2.36pm saying: “The AO Heat Stress Scale is above 5.0. Play is suspended for all matches and practice on outside courts. The roofs on RLA [Rod Laver Arena], MCA [Margaret Court Arena] and JCA [John Cain Arena] will close and remain closed for the remainder of the match. If onsite, please seek shade and apply cooling strategies.”

The scale is based on radiant heat, humidity, air temperature and wind speed. When a level 4 is reached, a 10-minute break between sets, once per match, is introduced. When the scale reaches 5, the roof is closed or – if a match is on an outer court – play is suspended.

Sinner had already looked off his game before he began cramping and dropped the first set against Spizzirri. The Italian was applying multiple ice packs during changeovers and using a personal air conditioner while seated. During his fourth-round match at last year’s tournament, Sinner appeared to suffer from heat exhaustion, but still managed to beat Holger Rune in four sets.

With the roof closed and the temperature in Rod Laver Arena back in the 20Cs, Sinner booked his place in the fourth round, winning 4-6, 6-3, 6-4, 6-4 in close to four hours.

Earlier, the defending women’s singles champion, Madison Keys, brushed past Karolina Pliskova 6-3, 6-3 in just 75 minutes to book a last 16 clash against Jessica Pegula. The American said although she was ready for the heat, she gave herself a “pat on the back” for navigating a match against the former world No 1 with the minimum of fuss. “I was excited for the heat today. Being a Floridian, I was ready for it,” Keys said. “Overall, I’m feeling really good and happy to have some clean matches.”

Anticipating heat delays, officials brought forward the start of play by 30 minutes on Saturday. The Bureau of Meteorology forecast was for a top of 40C at 5pm, with the mercury rising rapidly in the early afternoon. The temperature was tipped to be 38C as late as 8pm.

Just after midday, before Sinner’s match against Spizzirri, the temperature was 32C. But by 1pm the temperature was climbing and the heat stress scale had reached 3.2. An hour later it had already exceeded 4, triggering a 10-minute break between the third and fourth sets, before it passed 5 about 30 minutes later.

Alex De Minaur, after his victory over Frances Tiafoe on Friday night, said the heat “is going to be a lot”. “You’ve got to make sure that you hydrate, you eat well, you recover well, make sure [you prepare] everything prior to the match, and as the match is going on, ice towels from the very first game,” he said.

“Make sure you stay in the shade as much as you can, and, yeah, get ready for feeling uncomfortable. But sometimes that’s part of tennis and is one of the factors that play into this beautiful game that we have.”

Officials are expecting crowds to be down on the middle Saturday – traditionally one of the tournament’s busiest days – due to the heat. As temperatures soared, the water misters and free sunscreen were proving popular.