Melbourne - Andy Murray has warned organisers were risking a tragedy on Tuesday as extreme temperatures caused players to faint and vomit in a day of extraordinary scenes at the Australian Open.
The Scot, who safely progressed alongside Roger Federer and Rafael Nadal, queried whether it was safe to play in temperatures which touched 42.2 Celsius.
"Whether it's safe or not, I don't know. You've just got to be very careful these days," said the world number four after his first-round win against Japan's Go Soeda.
"There's been some issues in other sports with, you know, players having heart attacks. I don't know exactly why that is. Or collapsing."
On one of the hottest days the tournament has ever seen, untoward incidents littered the day and overshadowed the conclusion of round one at Melbourne Park.
Federer, watched by new coach Stefan Edberg, was regal in his 6-4, 6-4, 6-2 win over Australia's James Duckworth, and Murray, who is returning from back surgery, overpowered Soeda 6-1, 6-1, 6-3.
In the comparative cool of the evening session, Nadal was given easy passage when mercurial home hope Bernard Tomic retired with a thigh injury when one set down.
"I felt really sorry for Bernard. I was in that situation a few years ago and I know how tough is to take that decision," said Nadal, who retired himself during the 2010 quarter-finals.
"But if you feel bad, there is no reason why you have to continue. You're risking the next tournaments for nothing."
In the women's draw, defending champion Victoria Azarenka beat Johanna Larsson and former world number one Caroline Wozniacki ousted Lourdes Dominguez Lino for the loss of just two games.
Maria Sharapova, still using ice vests in temperatures over 30 Celsius after 11:00 pm, beat Bethanie Mattek-Sands 6-3, 6-4.
And it was the severe heat that dominated discussion, after Canada's Frank Dancevic felt dizzy and then blacked out during his loss to Benoit Paire.
"I think it's inhumane, I don't think it's fair to anybody, to the players, to the fans, to the sport, when you see players pulling out of matches, passing out," he complained.
"I've played five-set matches all my life and being out there for a set-and-a-half and passing out with heat-stroke, it's not normal."
Meanwhile, a ball boy collapsed during Milos Raonic's win over Daniel Gimeno-Travers, and China's Peng Shuai cramped up and vomited before losing to Japan's Kumuri Nara.
"I had no energy, I couldn't run, I couldn't serve," she said, blaming the heat for her defeat. "So it's impossible to play tennis like this."
Officials said because humidity remained low, they chose not to invoke emergency rules which allow them to halt play and close the roofs on the centre and second court. Temperatures are set to remain above 40 Celsius for the next three days.
"Of course there were a few players who experienced heat-related illness or discomfort, but none required significant medical intervention after they had completed their match," said chief medical officer Tim Wood.
Japan's Kei Nishikori came through a thrilling five-setter with Marinko Matosevic, but Australian veteran Lleyton Hewitt was sent crashing despite going the distance with Italy's Andreas Seppi.
Former finalist Jo-Wilfried Tsonga went through smoothly against Filippo Volandri and Juan Martin del Potro won in four sets against America's Rhyne Williams.
Among the women, Polish fifth seed Agnieszka Radwanska progressed and America's Sloane Stephens, a semi-finalist last year, got off the mark in two sets against Kazakhstan's Yaroslava Shvedova.
In the stifling conditions, Polona Hercog was one of a number of retirements. The Slovak won only one point and was on court for 10 minutes before she pulled out with a right shoulder problem.