World number one Serena Williams was knocked out of the 2014 Australian Open by Ana Ivanovic on Day seven.
The Serb came back from a set down to win 4-6 6-3 6-3 in one hour and fifty-six minutes- her first ever victory over Williams in five attempts.
Williams complained of a back problem prior to the match and revealed she even considered pulling out of the game.
26-year-old Ivanovic now moves on to face Canada’s Eugenie Bouchard in the last eight.
It is the first time the Serbian will be reaching the quarter-final of a Grand Slam since winning the 2008 Roland Garros women’s singles.
The reigning French and US Open champion had been tipped to win all four major Grand Slams in 2014 by her coach but it was the 14th seed that showed determination and zeal early into the three-set match.
Ivanovic withstood the 32-year-old American’s powerful serves, fashioned four break points in the first set- concerting one- on her way to losing 4-6 after being broken twice by the top seed.
The 14th seed Serbian stepped on her gas pedal in the second as Williams appeared to start struggling with her movement in court.
Her serves held up well and she didin’t face another break point thereafter.
On the other end of the Rod Laver Arena court, Williams was warned for time wasting and when she only managed to save two match points before Ivanovic closed it out with a love.
Serena Williams said: “I almost pulled out. I’m such a competitor, I probably should have.
“I don’t want to blame anything. I feel like Ana deserves all the credit. I feel she played unbelievable today. I think she went for her shots.
“It’s not anything that’s life threatening or anything. I feel like it will get better. I just need a couple days off.
“Unfortunately I don’t have that in a Grand Slam.”
Ivanovic said: It’s amazing. Honestly, I went on the court and I just wanted to play the best I could. I’m so thrilled.
“I was very consistent.
“It’s not easy playing such a champion, but she’s also just a human and I know she has lots of pressure too.
“I just went out there swinging and I think I did that really well.”
On winning four Grand Slam titles in 2004, the American added: “I have given up on that a long time ago. I feel like I don’t even think about winning four in a row.
“Maybe I can win four in a row, but it seems like in the one year it’s kind of difficult for me for whatever reason.”