The extreme heat policy was invoked at 1345 local (0245 GMT), with air temperatures soaring above 40 degrees Celsius.

Play on the main Rod Laver Arena court between second seed Serena Williams and eighth seed Svetlana Kuznetsova was suspended at the end of the first set, won by Kuznetsova 7-5, to allow them to close the roof.

The roof takes 25 minutes to close. All matches on outside courts were also suspended and no new matches would be called until a new reading is conducted at 1445.

Organisers use a complicated formula that combines the air temperature, wind, solar radiation and humidity to achieve a Wet Bulb Globe Temperature (WBGT) reading.

Once the WBGT threshold is reached, match referee Wayne McKewen then determines whether or not to suspend play. The threshold is not made public.

Dementieva beats Navarro and heat to reach semis

Russia's Elena Dementieva battled her way through brutal conditions to beat unseeded Spaniard Carla Suarez Navarro 6-2 6-2 in the quarter-finals of the Australian Open on Wednesday.

Both players struggled in the scorching heat as the temperature approached 40 degrees Celsius but it was the more experienced Dementieva who coped best.

The world number four won the first four games to runaway with the opening set, then raced to a 5-1 lead in the second to wrap up victory in 93 minutes.

"It was very tough to play because of the weather conditions," Dementieva said.

"Maybe it looked easy but I think for such a score like 6-2 6-2, we played one and a half hours, which is a pretty long match.

"She is very strong physically, a very fit player. Playing for the first time, I didn't know what to expect from her."

Despite the lopsided scoreline, Dementieva did not have it all her own way against the Spanish baseliner, who enhanced her reputation as one of the rising stars of women's tennis by reaching her second grand slam quarter-final in only four tournaments.

Break Points

Dementieva served 10 double-faults and had to fight off 10 break points on her own serve, twice as many as Suarez Navarro offered up.

"I had a lot of break points but I couldn't take them," the Spaniard said.

Dementieva has never won a grand slam singles title but has been in great form over the last 12 months, winning the gold medal at the Beijing Olympics and making the semi-finals at Wimbledon and the U.S. Open.

The 27-year-old spent the off-season training in Florida to get herself in the best possible shape for Australia although she said there was nothing she could do to fully prepare for the extreme temperatures.

"You can work so hard trying to get ready for the weather conditions but when you have to face 40 or 41 (degrees), there is no way you can get used to it," she said.

"The best way is to play as quick as possible and just get away from the court. There is no way to adjust with the heat here."

"The plan was just to step into the court, just try to be aggressive and make winners."

Dementieva's hard work has already paid off this season, she won two warm-up tournaments in Auckland and Sydney and Wednesday's win over Suarez Navarro extended her unbeaten run this year to 15 matches.