By Alastair Himmer

MELBOURNE (Reuters) - Former world number one Maria Sharapova suffered a shock fourth round defeat at the Australian Open on Sunday, bundled out 6-2 6-3 by bottom-wiggling German Andrea Petkovic.

Bosnian-born Petkovic celebrated reaching the last eight of a major for the first time with an on-court jig.

"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 quarter-finals.

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 2-0 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 a rueful Sharapova, who since winning here three years ago has reached just one grand slam quarter-final.

"Last year I was gone on Monday. I stayed here a little bit longer this year.

"But there are many things that didn't work today. I didn't get my first break point until it was a set and 5-1. That's not the type of tennis I want to be playing."

(Editing by Martyn Herman)