Fourth seed Maria Sharapova has survived her toughest test yet at this year's Australian Open to fight her way into the quarter finals with a gritty straight sets win over Daniela Hantuchova.

Maria ground out a 6-4, 6-4 victory in 1hr 37 mins to ensure the 17th seed Slovak, who dumped defending champion Serena Williams from the tournament, did not repeat her giant-killing feat. The Russian was broken in her first service game and said she started the match sluggishly on a hot Melbourne night. "Today was probably one of the hottest days I've ever experienced in my life. I mean, it was pretty brutal out there," she said, describing the Australian Open as the most physically demanding of the tour's four Grand Slams.

"I just kept calm and tried to break her and tried to get the momentum back and it went my way in the end," said the former Wimbledon champion, who almost skipped the tournament because of a rib injury. But she declared she was now approaching peak form and was excited to reach the quarter-finals of a tournament she had feared she would miss. "Little by little I am," she said. "It was good today, I kept my composure when I was down at the beginning of both of the sets." "You just hope for the best and hope that you get better and better as the matches go on -- I feel like that's been happening.

"I feel like I've been improving with every match. Every match has been getting a little bit tougher and different." Hantuchova, 22, said she pulled a muscle in her left leg while racing to a second set lead and her movement was restricted when she resumed playing after having her thigh strapped.

But the former world number five, who is rebuilding her career after her ranking went into freefall in 2003, said she left the tournament feeling her comeback was on track after beating seven-time Grand Slam winner Williams. "I'm taking home some really nice memories, especially from the match against Serena," she said. "It was something very special for me. "Today I felt, again, that I was very close. But it just showed me the few little things that I still need to work on and improve. Hopefully next time I come back here, I will be even more ready."

Maria will next meet her compatriot, sixth seed Nadia Petrova, who defeated her in their last meeting.