Former world No. 1 Maria Sharapova suffered a shock fourth round defeat at the Australian Open yesterday, bundled out 2-6, 3-6 by bottom-wiggling German Andrea Petkovic.

In another upset of the day, Andy Roddick lost to Stanislas Wawrinka, meaning there'll be no Americans in the men's or women's quarterfinals.

Sharapova committed 30 unforced errors in a performance which underlined her struggles since shoulder surgery in 2008, the year she won the last of her three grand slam titles in Melbourne.

The Bosnia-born political science student, who defied her parents to pursue a tennis career, has also been winning over crowds with her bright smile and her on-court jig that has come to be known as "The Petko."

"It started off as a bet with my coach," Petkovic told reporters of the cheeky dance of delight she performed after her upset win.

"I'm very superstitious and since I started doing the dance I'm playing much better, so I'll try to keep it up," added the 23-year-old, who faces China's Li Na in the quarterfinals.

Squealing mightily on every shot, 14th seed Sharapova could do little right in the first set, spraying wild shots all over Rod Laver Arena. The Russian showed a few signs of a possible fightback during the second set after going 0-2 down but the hole she had dug for herself was too big against a dangerous opponent.

She fended off two match points with a pair of rocket forehand returns but Petkovic completed victory in 79 minutes with a deep serve Sharapova could only push into the net.

"It definitely wasn't there," said Sharapova, who has reached just one grand slam quarterfinal in the last three years. "Last year I was gone on Monday. I stayed here a little bit longer this year.

Wawrinka's 6-3, 6-4, 6-4 win means two Swiss men will meet in a major quarterfinal for the first time in the Open era - he'll face defending champion Roger Federer, who matched the record for most consecutive appearances in the last eight at grand slams.

Federer beat Tommy Robredo 6-3, 3-6, 6-3, 6-2 to reach the quarterfinals for the 27th major in a row.

French Open champion Francesca Schiavone established a grand slam record, needing 4 hours, 44 minutes - the longest at a grand slam - for her 6-4, 1-6, 16-14 fourth-round win over Svetlana Kuznetsova.

Kuznetsova said the match was so long she was forgetting the score or who should serve.

No. 3-ranked Novak Djokovic advanced to the quarterfinals for the 13th time in the last 15 majors with a 6-3, 6-4, 6-0 win over No. 14 Nicolas Almagro and will next play last year's Wimbledon finalist Tomas Berdych, who beat Fernando Verdasco 6-4, 6-2, 6-3.