Ivanovic had never won a set against Williams in four previous meetings with the American, who came into the clash on a 25-match winning streak and the undeniable favourite.

These stats did nothing to faze the former world number one who, after a tentative first set, secured by far the biggest shock of the tournament with a tremendous display at the Rod Laver Arena, eventually winning the contest 4-6, 6-3, 6-3.

"It's amazing," said the 14th seed.

"Honestly, I went on the court and I just wanted to play the best I could.

"I'm so thrilled."

While Williams went to great lengths to pay tribute to Ivanovic and not make excuses for her loss, her coach, Patrick Mouratoglou, revealed that the top seed was struggling with a back complaint.

A problem so bad Williams was unable to carry her own bag onto court.

"I don't want to blame anything," she said.

"I feel like Ana deserves all the credit.

"I feel she played unbelievable today.

"I think she went for her shots.

"It's not like I gave her the match.

"I tried to fight the best I could today."

Serbia's Ana Ivanovic pulled off the shock of the tournament by beating world number one Serena Williams in the fourth round of the Australian Open ©Getty Images


Ivanovic's next challenge will see her face Canadian Eugenie Bouchard, who knocked out local favourite Casey Dellacqua in three sets, 6-7, 6-2, 6-0.

She will be joined in the last eight by former French Open champions China's Li Na and Italian surprise package Flavia Pennetta.

Li breezed past Russia's Ekaterina Makarova 6-2, 6-0 in just 59 minutes to record one the quickest matches of the day, while Pennetta continued her fine form to oust Germany's Angelique Kerber following a first set loss in just 21 minutes.

On the men's side, Serbian Novak Djokovic edged a step closer to his fourth straight Australian Open title and fifth in all, with a straight sets victory - 6-3, 6-0, 6-2 - over Italian Fabio Fognini.

Djokovic will now face Stanislas Wawrinka in the quarter-finals following the Swiss man's straight sets victory over Spain's Tommy Robredo.

Novak Djokovic moved a step closer to his fourth Australian Open title with a win over Fabio Fognini ©Getty Images

David Ferrer came from a set down to battle past German Florian Mayer in four sets, 6-7, 7-5, 6-2, 6-1.

The Spaniard had to dig deep to recover from a tough first set but saw vast improvements as the match progressed.

He will now face Tomáš Berdych, who breezed past South Africa's Kevin Anderson, in his ninth consecutive Grand Slam quarterfinal.

The big Czech should prove a much tougher test for Ferrer, however, having not dropped a single service game in his first four matches in Melbourne.

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