Maria Sharapova and Kim Clijsters needed iron willpower to stagger through scrappy Australian Open quarter-finals on Wednesday and set up a heavyweight meeting in the last four.

• Images from Day 9

Top seed Sharapova struggled past fellow Russian Anna Chakvetadze 7-6, 7-5 in the opening match on Rod Laver Arena before fourth seed Clijsters dug deep to overcome her good friend Martina Hingis 3-6, 6-4, 6-3.

The match against sixth seed Hingis never lived up to expectations in terms of quality, and Belgian Clijsters needed great determination to overcome 62 unforced errors and extend her last Australian Open campaign with victory over the three-times former champion.

"I wasn't really seeing the ball," Clijsters said in a courtside interview. "The only thing you can do is fight and hope you can turn things around and I did.

"I have to be sharp against Maria, she's an incredible athlete and fights for every point. Hopefully, I will hit less than 62 unforced errors."

Hingis looked on course to beat Clijsters for the first time since 2002 when she took the first set and she had the Belgian on the ropes in the second.

Clijsters had not dropped a set in a swaggering march to the quarter-finals but she simply could not shake off the Swiss as a stream of unforced errors and double faults flew off her racket.

TIRE OUT

But roared on by the crowd Clijsters gradually asserted herself and played a succession of deft drop shots to tire out her an opponent three years her senior.

Hingis ran out of steam in the third set and Clijsters pounced, sealing victory in just over two hours with a forehand winner down the line before the pair embraced warmly at the net.

The 19-year-old Sharapova, who will be world number one next week, was broken twice in each set and failed to find any rhythm against her 12th-seeded compatriot.

"I thought I was up and down, a bit scratchy," Sharapova said after dispatching her third fellow countrywoman of the tournament in an unconvincing run to the last four.

"When you're a set and a break up it's still tough, I'm glad I got through."

Unseeded American Serena Williams, twice former champion at Melbourne Park, plays Czech 10th seed Nicola Vaidisova in the other semi-final on Thursday.

In Wednesday's men's quarter-finals, third seed Nikolay Davydenko meets number 12 Tommy Haas of Germany and number two Rafael Nadal takes on in-form Chilean Fernando Gonzalez, seeded 10th.

World number one Roger Federer plays sixth seed Andy Roddick in the other semi-final on Friday.