The German 21st seed, fresh from beating world number one Caroline Wozniacki a day earlier, continued to display her exciting promise with a 2-6, 6-2, 6-4 triumph over Serbian Jankovic.

In a fourth round match, world number two Clijsters staved off five match points before edging out Ana Ivanovic 7-6, 3-6, 7-6 to keep her title defence alive.

Russian Maria Sharapova emerged from a compelling three-hour 28 minute battle with Romanian Alexandra Dulgheru which ended 3-6, 7-6, 7-6.

With some gutsy play from the baseline, the energetic Petkovic turned things around in the second set, saving four break points with her improving serve.

Jankovic fought back in the third, building a 4-2 lead, but Petkovic reeled off four games in a row to finish it, including a thrilling seven-deuce final game.

Petkovic will face Sharapova after the 16th seed narrowly defeated a determined Dulgheru, who played some superb defensive tennis.  Sharapova had to receive medical attention shortly after breaking to go 5-4 up in third, a nasty turn of the ankle leaving her in clear pain.

The dogged Romanian, then, broke back and there were some tremendous rallies in the tie-break before Sharapova finally triumphed to set up a chance of revenge for her fourth round defeat to Petkovic at the Australian Open in January.

While the 23-year-old Petkovic celebrated her place in the final four with her trademark ‘Petko Dance’, Ivanovic was reduced to banging rackets after yet another reminder of the Serb’s frequent inability to finish off matches.

The game, delayed by rain from Monday, was there for the taking at 5-1 when Ivanovic failed to convert four match points and she squandered another opportunity at 5-3 before losing the deciding tie-break.

Top seeds Rafael Nadal, Roger Federer and Novak Djokovic all cruised into the quarterfinals in the men’s event with straight sets victories on Tuesday.  After rain delays earlier in the day, Federer took to the court at 12.40 am local time but made short work of Belgian Olivier Rochus, winning 6-3, 6-1 in just 52 minutes.

Federer, who faces Frenchman Gilles Simon next, will meet Nadal in the semifinals should they both progress.  Nadal had a similarly easy match, facing virtually no resistance from Ukrainian Alexandr Dolgopolov in a 6-1, 6-2 victory, winning 86 percent of first service points without facing a single break point.

The Spanish world number one will meet Czech Tomas Berdych, a 6-3, 2-6, 7-6 victor over German Florian Mayer, in the quarterfinals.  Djokovic remains unbeaten in 2011, chalking up 21 successive wins, and that record was never in danger against fellow Serb Viktor Troicki in a straightforward 6-3, 6-2 win.

The world number two was comfortable throughout and will now face South African Kevin Anderson in the last eight -- a player he lost to in this tournament three years ago.
Argentina’s Juan Martin Del Potro, still making his way back from lengthy injury problems, fell to American Mardy Fish 7-5, 7-6.

Fish is now one win away from replacing Andy Roddick as the top ranked American after his hard-fought victory in front of a crowd that was heavily backing his opponent.  Fish will overtake Roddick, who lost in his opening match here, should he beat Spain’s David Ferrer in the quarterfinals.