Sixth-seeded Mirza was one of only two seeds remaining in the main draw at the start of the tournament’s third day but, by the end, No 2 Vera Zvonareva was left alone among seeded players.

Pennetta converted five of eight break point chances and survived a mid-match slump on her way to a gritty win. “It was not a very good match for people to watch,” Pennetta said. “There were a lot of mistakes from both players.”

Zvonareva beat Russian compatriot Elena Vesnina 6-3, 6-3, keeping up the strong form she has shown throughout the tournament.

Zvonareva has a semi-final against Ashley Harkleroad, a 6-4, 6-4 winner over Edina Gallovits of Romania in a clash of qualifiers.

Harkleroad let two match points slip before clinching a win over Gallovits which propelled her into her third WTA semi-final.

Pennetta’s semi-final opponent will be Eleni Daniilidou of Greece, who beat Australian wildcard entry Casey Dellacqua 6-4, 7-5.

Meanwhile, doubles ace Mahesh Bhupathi also crashed out of the $4,65,000 Medibank International after going down in straight sets in the first round in Sydney. Bhupathi, partnering Mark Knowles of Bahamas, lost 4-6, 4-6 to the Czech pair of Tomas Berdych and Radek Stepanek.

Nalbandian ill

•Melbourne: A frustrated David Nalbandian is fighting to be fit for next week’s Australian Open after pulling out of the warm-up event at Kooyong because of a back injury.

The Argentine, who ended last year by winning back-to-back Masters Series titles in Madrid and Paris, suffered back spasms during a practice session at Melbourne Park on Wednesday.

Nalbandian will have an MRI scan on the injury later in the day but has been told to rest for at least three days, leaving him just a couple of days to prepare for the first Grand Slam event of the year. “I think I am going to be OK, but you never know,” Nalbandian said.

“I had what they say is a distension in the back. I have four, five days to go. I will try to hit on Saturday for 30-40 minutes and see how it is.”

Nalbandian was considered one of the favourites for the title at Melbourne Park, having ended the season on a high with his back-to-back Masters Series wins. The world number nine was practising with former number one Marat Safin of Russia when he first felt pain.