'Toughest conditions I've played in'

(CNN) -- The toughest conditions she has ever played in. That's how one of tennis' biggest stars described this year's scorched Australian Open.

And it's not hard to see why.

With temperatures in excess of 40 degrees, and after four days of players fainting, vomiting and tirelessly icing themselves to keep cool, Li Na was feeling hot and flustered.

The fourth seed, a runner-up at last year's Melbourne grand slam, was facing match point and a shock early exit at the hands of world No. 26 Lucie Safarova.

But the Czech sent a backhand five centimeters long of the baseline, letting Li back in to take a second-set tie break and then take advantage of the extreme heat contingency plan.

In light of the oppressive weather, tournament organizers have allowed for an extra 10 minutes between the second and third sets of women's matches, a break which rejuvenated the 2011 French Open champion.

Read: Del Potro feels the heat in Melbourne

"After the second set, lucky thing we had the 10 minute break," China's Li told reporters after her 1-6 7-6 (7-2) 6-3 victory set up a fourth round match with Russia Ekaterina Makarova.

"I think five centimeters saved my tournament. If she hit it in, I think me and my whole team would be on our way to the airport now.

"At least I won the match, and I'm still in the tournament now. It was a difficult day for me but I was really happy with the way I was fighting on the court from the first point until the last point."

While Li Na went to cool down, tournament doctor Tim Wood had defended organizers' refusal to halt play during the sunniest parts of the day, saying that, while playing in the heat might be terribly uncomfortable, human beings "evolved on the high plains of Africa chasing antelope for eight hours under these conditions.

"There will be some players who complain and no-one is saying it is terribly comfortable to play out there, but, from a medical perspective, we know that man is well adapted to exercising in the heat. Whether it is humane or not is a whole other issue," Wood told the BBC.

Words that might not be music to Britain's Jamie Murray's ears, who was treated for heatstroke.

Whatever the conditions, world No. 1 Serena Williams continues her peerless dominance of the women's game.

The top seed has now won more matches at the Australian Open than any other woman in history after registering her 61st success at Melbourne Park by beating Daniela Hantuchova 6-3 6-3.

"I feel good to have gotten through that one because it was tough conditions out there, but I was happy to win," said the 32-year-old.

"Today actually wasn't as hot. I think it was hotter yesterday. So it wasn't as bad today. Honestly, on the one end I felt it was like a cool breeze coming over, so that was a good sign."

Williams' fourth round opponent will be the resurgent Ana Ivanovic, who reached the fourth round after coming from one set down to end Australian Samantha Stosur's hopes of a home grand slam triumph.

In the men's draw, defending champion Novak Djokovic remained on course for his fourth Australian Open title in a row as he eased into the fourth round with a 6-3 6-3 7-5 victory over Denis Istomin of Uzbekistan.

"I feel better on the court as the tournament is progressing," Djokovic, who played under the cool conditions of the Rod Laver Arena's closed roof, told reporters.

"Of course, I played three matches in different conditions. The roof was closed and the temperature dropped by at least 10 degrees, and you could feel that. It affected the play, it was much slower."

Victory for the Serbian, who won his first grand slam in Melbourne in 2008, sets up a meeting with his old friend Fabio Fognini, after the Italian beat American Sam Querrey.

"I'm going to try to win against him regardless of whether he's a friend or not," Djokovic continued. "I have a real friendship with him for more than 10 years but once we get on court we're both professionals and we want to win."

Spanish third seed David Ferrer, Tomas Berdych, the Czech seventh seed, and South African Kevin Anderson also booked their places in the next round of the sizzling Australian Open.

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