Li Na had one simple request before answering questions in her on-court, post-match interview after battling for 2½ hours in the brutal heat at the Australian Open on Friday: "Can we stand in the shadow?"

The Chinese star certainly earned the courtesy. She saved a match point before prevailing against Lucie Safarova, all while playing at the hottest time of the day.

The temperature topped 40C (104F) for the fourth consecutive day in Melbourne, the longest heat wave in the city for more than a century.

Players draped themselves with ice packs during changeovers and those in the women's singles were given a 10-minute break before playing a third set, but tournament officials did not enact the "Extreme Heat Policy," which would have suspended matches on the outer courts and closed the roofs on the two show courts.

The heat policy was put into effect on Thursday when the temperature reached 42C (108F) in the early afternoon, suspending matches on the outer courts for about four hours.

The high again topped 42C (108F) on Friday, though the humidity was lower than in previous days.

Some players, again, struggled in the stifling conditions. China's Zheng Jie received medical treatment after she indicated she was dizzy and struggling with her breathing during the second set of her third-round loss to Casey Dellacqua. A doctor checked her blood pressure, as she was lying across chairs beside the court. She got up and broke Dellacqua's serve in the next game, but lost the match.

Poland's Jerzy Janowicz, the 20th seed, looked completely drained during his third-round loss to Germany's Florian Mayer and said later, holding back tears, that his only chance would have been to play at night.

"Whatever he would do today and whatever I would do today doesn't matter," he said. "I had no power to stay on the court. I felt like I'm going to collapse soon."

Top-seeded Serena Williams had an easier time during her 80-minute win over Daniela Hantuchova but she, too, sought any shade she could between points and later withdrew from the doubles competition with sister Venus before they were scheduled to play their first-round match.

The official reason was an injury to Venus' leg, but Serena admitted she didn't relish the idea of playing another match in the heat.

"I guess it's a relief, but like I say, we love to play doubles and we love to be out there," she said.

Although players have blacked out, staggered, hallucinated and vomited on court this week, tournament officials have defended their decision to only halt play once during the four-day heat wave.

Speaking to BBC radio, tournament doctor Tim Wood said that while it may not be "terribly comfortable" to play in these conditions, it's safe from a medical perspective.

"We know that man is well-adapted to exercising in the heat. If you take us back a few thousand years, we evolved on the high plains of Africa chasing antelope for eight hours under these conditions," he was quoted as saying.

Andy Murray, whose brother Jamie received treatment for a heat-related illness and cramping after his doubles match on Thursday, said part of the problem has been the confusion surrounding the heat policy this week.

"It's weighing out whether or not it's kind of worth playing like that and it's worth it for the fans and everyone," he said after his second-round win late Thursday. "I've seen a lot of matches where everyone's kind of left and gone home. That's not good either."