An inspired Ana Ivanovic has blown the race for the Australian Open women's title wide open after stunning overwhelming favourite Serena Williams in the fourth round at Melbourne Park.
After the match it was revealed that Williams' quest for a sixth Australian title had been bedevilled by a back injury although the world number one and first seed didn't offer that as an excuse for the loss.
Williams was riding high on a winning streak of 25 matches going back to the start of last year's US Open and had not lost a single set to Ivanovic in four previous meetings.
But after losing the first set, Ivanovic started to play her ground strokes with confidence as the American's footwork began to falter.
The Serbian 14th seed was unflappable as her opponent stared angrily at her supporters box for answers.
None came as the 33-year-old winner of 17 major trophies was dispatched in three sets by the 26-year-old, 4-6 6-3 6-3.
Earlier, Italian player Flavia Pennetta upset the ninth seed Angelique Kerber in three sets to progress to the quarter-finals.
Pennetta next faces fourth seed Li Na of China, who wasn't troubled by her fourth round opponent, Ekaterina Makarova, ousting the Russian in straight sets.
In the men's draw, Novak Djokovic was forced to cede the spotlight to his Serbian compatriot Ivanovic, but showed no signs of relinquishing his iron grip on the men's title as he flogged Italian Fabio Fognini in straight sets, 6-3 6-0 6-2.
Third seed David Ferrer also advanced to the last eight and a meeting with Tomas Berdych , while women's fourth seed Li Na and Flavia Pennetta set up a last eight clash of 31-year-olds.