(CNN) -- The heatwave may have passed at the Australian Open but in its place came shockwaves as women's title favourite Serena Williams crashed out.
The American world No.1 melted under pressure from resurgent Serbian Ana Ivanovic in the fourth round Sunday.
Williams, who was chasing a sixth Australian Open crown and an 18th career grand slam, blamed the shock 6-4 3-6 3-6 defeat on an error-strewn display.
"I made a tremendous amount of errors, shots I missed I normally don't miss, I haven't missed since the Eighties," Williams told reporters. "I'm just not used to missing those shots.
"I just made way, way, a lot of unforced errors.
"I know for a fact I can play so much better than what I did today, so with that, knowing that, I'm not disappointed or anything. I just know that I can play ten times better."
Williams refused to blame a back injury for her defeat although the 32-year-old did reveal that she had considered quitting the opening grand slam of the year before her match against Ivanovic.
"I almost pulled out," explained Williams, who last lost a match in August. "I'm such a competitor. I mean, I probably should have.
"Maybe I wasn't the best physically, but that had nothing to do with it. I don't want to blame anything.
"I feel like Ana deserves all the credit. I feel she played unbelievable today. "
Victory for Ivanovic is a major boost for the 2008 French Open champion who is trying to get her career back on track after several seasons plagued by big-match nerves, serving troubles and a series of injuries.
The 26-year-old told CNN's Open Court last month that she had effectively pressed the re-set button ahead of the 2014 season, swapping British coach Nigel Sears for new coach and hitting partner Nemanja Kontic.
"I've been working really hard," said Ivanovic, who last reached a grand slam quarterfinal at the 2012 U.S Open. "I have a new team with me since Wimbledon and it's a Serbian team for me for the first time."
The restructure appears to be working as Ivanovic won a warm-up tournament in Auckland -- incidentally beating Venus Williams -- before notching up her first-ever win over Williams' younger sister Serena.
Asked by reporters in Melbourne what the difference was between this match and her previous encounters with Williams, she said: "Well, I actually believed. I had some confidence coming into today's match.
"This victory means so much to me. All the hard work, it's paying off.
"I had very tough fourth round matches in a grand slam, and this was probably the toughest of tough. I just went out there to play. I had nothing to lose.
"To have that victory, you know, it's amazing. We all know what kind of champion she is."
Ivanovic goes on to meet Canadian Eugenie Bouchard in the quarterfinals and, after her giant-slaying performance against Williams, the Serbian 14th seed might just feel she has a chance of going all the way.
In the men's draw, Ivanovic's childhood friend Novak Djovkovic eased into the quarterfinals with a straightforward 6-3 6-0 6-2 win over another close pal Italian Fabio Fognini.
Djokovic, who said he had managed to watch two sets of Ivanovic's match before taking to the court, faces Swiss Stanislas Wawrinka next, who took him to five sets in the fourth round of last year's Aussie Open.
"I have to be ready to play another 12-10 in the fifth like last year," Djokovic said. "I know that he's playing the tennis of his life in the last 15 months.
"You cannot expect a clear favorite in that match."
In the same half of the draw, Czech Tomas Berdych also advanced to the quarterfinals where he meets Spanish third seed David Ferrer.