Serena Williams was sensationally dumped out of the Australian Open in the fourth round by a resurgent Ana Ivanovic.
Ivanovic had failed even to win a set in four previous clashes against Williams, who was on a 25-match winning streak, but the 14th seed produced a stunning display to triumph 4-6 6-3 6-2.
Williams' coach Patrick Mouratoglou had said before the tournament he thought she could win all four grand slams this year, but instead the 32-year-old has again suffered a shock defeat in Melbourne.
Two years ago the world number one also lost in the fourth round to Ekaterina Makarova while last year Williams was beaten by fellow American Sloane Stephens in the quarter-finals.
Ivanovic said: "It's amazing, I'm so thrilled. It's not easy playing such a champion. But she's also human and I know she has a lot of pressure. I really went out there swinging."
There were reports prior to the match that Williams was struggling with a back problem, and the 32-year-old certainly looked out of sorts from the start.
Ivanovic broke the Williams serve for only the second time in the tournament in the fifth game but then dropped her own serve to love.
And when the Serbian served to stay in the set, Williams pounced, clinching it when Ivanovic netted a forehand.
When Ivanovic won the French Open in 2008, it seemed it would be first of many grand slam titles, but expectation and injuries got the better of the 26-year-old and she has spent the intervening years rebuilding her confidence.
Ivanovic was hugely impressive in beating home favourite Sam Stosur in the third round, and she showed she would not be intimidated by Williams by breaking serve again for 3-2 in the second set and this time cementing it with a service hold.
She had more chances to break in Williams' next service game as she used the world number one's power against her to great effect, but this time the American held on.
Ivanovic did not let it affect her, though, and took her third set point with a thumping forehand and a pump of the fist.
She then roared into a 3-0 lead at the start of the third set and it was all Williams could do to hang on.
Ivanovic had her first match point in the eighth game but netted a forehand going for a winner and Williams forced her to serve it out.
That proved no problem, though, Ivanovic bringing up three more match points and taking the first when Williams dumped a forehand long.
Ivanovic put her hands on her head in apparent disbelief as the Rod Laver Arena crowd hailed her achievement while Williams quickly trudged off court.
Ivanovic, a finalist at Melbourne Park as a 20-year-old in 2008, is through to just her second grand slam quarter-final since her French Open triumph and next meets either Australia's Casey Dellacqua or Eugenie Bouchard of Canada.