* Sharapova through after three-set marathon
* Russian suffers in heat before victory (Writes through, adds byline)
By Ian Ransom
MELBOURNE, Jan 16 (Reuters) - Maria Sharapova criticised Australian Open organisers for a lack of transparency over their 'extreme heat policy' when the Russian was left toiling on court for nearly an hour after organisers had invoked an official halt on Thursday.
Sharapova and her opponent Karin Knapp of Italy slugged it out in 40 degrees Celsius (104 Fahrenheit) heat at Rod Laver Arena for three-and-a-half hours before the Russian prevailed 6-3 4-6 10-8 in their marathon second round encounter.
The pair were already struggling in the oppressive conditions but continued their arduous battle some 50 minutes after matches on outside courts were suspended at about 1:50 p.m. local time (0250 GMT).
Players have slammed organisers for failing to call off matches earlier, with some describing the conditions as dangerous, and one Croatian player in the men's draw expressing fear for his life on Wednesday.
Rather than use the raw Celsius readings to assess the heat, organisers prefer to use the Wet Bulb Global Temperature composite, which also gauges humidity and wind to identify the perceived conditions.
Under a change to the rules for this year, the decision on whether to stop matches is now at the discretion of tournament referee Wayne McKewen.
"There is no way getting around the fact that the conditions were extremely difficult, and have been for the last few days," the third seed Sharapova told reporters.
"It's a tough call. I mean, I think the question I have is no one really knows what the limit is.
"Not the players (nor) the trainers themselves when you ask them when will the roof be closed.
"No one actually knows what that number is in comparison to humidity or the actual heat.
"Sometimes you wish you knew, because it's - it just depends on I'm not sure who, a referee or the meteorologist, and there are just a lot of questions in the air that maybe should be solved.
"I asked the trainer the other day, 'what does it take for the roof to be closed or matches to be stopped?' She said, 'we have no control over this'."
Despite the suspension, players could only walk off court at the conclusion of the set they were playing, according to the policy.
With no tiebreaks in deciding third sets for the women entrants at the Australian Open, nor for fifth sets for the men, Sharapova and Knapp's battle continued well after the suspension was called, with Rod Laver Arena's retractable roof left open.
"I think the question is from the second to the third set," Sharapova said of the unused roof.
"That's because everyone knows there is no tiebreaker in the third set, so once you start that set, you're going to be out there until you're done. That's the question I have.
"I would love to know a bit more detail before - not even before I get on the court, but just in general it's good to know. I didn't even know there was no play when I left the court. I mean, I had no idea."
Sharapova, who will meet 25th-seeded Frenchwoman Alize Cornet in the third round, joked that she was getting "numb" to the heat in her courtside interview but will surely look forward to far cooler temperatures forecast for the weekend.
"I'm really happy to get through," she said. "I really am. I worked really hard in the last few months and I wanted this match. I didn't play my best tennis, I didn't do many things well."
"I got through it and sometimes that's what's important." (Additional reporting by Greg Stutchbury; Editing by John O'Brien)