MELBOURNE, Jan 27 (Reuters) - Australian Open organisers invoked their extreme heat policy as temperatures soared at Melbourne Park on Tuesday, prompting the suspension of play on outer courts and the closure of roofs on the main showcourts.
The tournament's "Heat Stress Scale" reached the highest threshold of 5.0 early in the afternoon with the temperature breaking through the 40 Celsius (104F) mark by 2 p.m. -- the hottest day of the tournament so far.
The year's opening Grand Slam operates under an extreme heat policy that considers air temperature, radiant heat, wind speed and humidity to assess playing conditions.
The threshold was reached soon after world number one Aryna Sabalenka completed her 6-3 6-0 win over American teenager Iva Jovic, with the roof on the Rod Laver Arena closing as the players left the court.
"At the end of the match, it was really hot out there," Sabalenka told reporters. "I'm glad they closed the roof almost halfway so we had a lot of shade in the back, so we could go back and stay in the shade.
"I knew going into this match that they won't let us play on crazy heat. If it (the scale) would reach the five, they would definitely close the roof, so I knew that they were protecting us, our health.
"Anyway, when we finished it was 4.4, so it was quite hot. It's okay, I'm happy that I managed."
The quarter-final match between third seed Alexander Zverev and 25th seed Learner Tien began under the roof at Rod Laver Arena.
The only other match that was being played at Melbourne Park was a mixed doubles quarter-final under the roof at Margaret Court Arena while practice was also suspended on the outer courts.
Organisers, players and fans alike have been bracing for another day of blistering heat, with temperatures forecast to hit the mid-40s later in the day.
Queues for entry into the venue were much shorter than usual and crowds were largely absent from concourses across the venue, where the latest edition of the season's opening Grand Slam has been watched by record numbers.
Matches in the Wheelchair Championships have been postponed by 24 hours due to the forecast heat with organisers advising fans to bring hats, drink plenty of water and make use of misting fans scattered around Melbourne Park.
Special conditions have also been put in place for tournament staff, with ball kids given shorter spells on court along with increased recovery times and additional relief squads.
(Reporting by Michael Church, Additional reporting by Rohith Nair in Bengaluru; Editing by Himani Sarkar and Peter Rutherford)
