Ivanovic, a fast upcoming tennis ace with a smile on her lips and concentrating on single tournaments, however, hadn't won a set in her four previous matches against Williams, who had been a hot favourite to win a sixth Australian Open crown for her 18th Grand Slam title.

The powerful serve that carried Serena Williams to 25 consecutive wins suddenly became the target of Ana Ivanovic's attack in a stunning fourth-round upset at the Australian Open. And Ana won it.

 
Serena won the first set  but Ivanovic  got the upper hand in the next two sets, the the No. 14-seeded Serb came back from a set down to win 4-6 6-3 6-3 - her first ever victory over Williams in five attempts. Ana Ivanovic setting up the win by attacking the best serves in women’s tennis. Ivanovic got on top early in the second set with some powerful forehand winners and never really let Williams back into the contest. She frequently stood well inside the baseline to receive, she took big swipes on her forehand and generally put Williams off her rhythm. “It’s not easy playing such a champion, but she is also just a human,” said Ivanovic.

 
Williams hit 22 winners but made 31 unforced errors, mostly on her backhand. Ivanovic had 33 winners, including 20 on her forehand. She also had some luck, when she drove a backhand off the top of the net and it looped onto the line.

 
The 2008 French Open champion had 33 winners, including 20 on her forehand side. Williams hit 22 winners but made 31 unforced errors, with most coming uncharacteristically on her backhand side. “I made a tremendous amount of errors, shots ... I haven’t missed since the ‘80s,” Williams said. It was her 70th match at Melbourne Park, a record in the Open era, and she’d already set the mark for most match wins ever at the Australian Open with her third-round victory.

The reigning French and US Open champion had been tipped by some to complete the Grand Slam of all four major titles in 2014."I have given up on that a long time ago," said the 32-year-old. "I feel like I don't even think about winning four in a row.

 
Williams said after being told her coach had released news of her back problem. “Again, I don’t want to blame anything. I feel like Ana deserves all the credit,” Williams added. “I feel she played unbelievable today. I think she went for her shots. It’s not like I gave her the match.”  Williams later admitted she’d been bothered by a back problem in practice in recent days and considered pulling out of the tournament.

 
Serena Williams sat before a bank of television cameras, below a gaggle of reporters, in both an unfamiliar and impossible position. There were no right answers, only question

Ivanovic is a former world number one and 2008 French Open champion, but since then she has reached just one major quarter-final at the 2012 US Open. A 0-4 record against Williams gave little cause for optimism either, but from the outset Ivanovic was able to threaten the American's usually impregnable serve.

 
Ivanovic had never taken a set off Williams in four previous matches, and Williams had only ever lost once after winning the first set at the Australian Open. The crowd was evenly divided at first but, sensing an upset, started backing Ivanovic, the former girlfriend of Australian golfer Adam Scott.

 
Earlier, Ivanovic defeated Serena’s sister Venus Williams in the final of the WTA event at Auckland, New Zealand earlier this month. “I just went out there swinging at the ball.”

 
Ivanovic advanced to a quarterfinal against the winner of match between Australian wild-card entry Casey Dellacqua and No. 30-seeded Eugenie Bouchard of Canada , who reached the last eight at a major for the first time after beating Australian wild-card entry Casey Dellacqua 6-7 (5), 6-2, 6-0..

Another Serb  and top player Novak Djokovic watched the second and third sets of fellow Serbian Ivanovic's win on TV, then continued his bid for a fourth straight Australian title with a 6-3, 6-0, 6-2 win over Fabio Fognini.

Ana Ivanovic would also enter the semifinals and hopefully would clinch the title as the Serena is already out and she can now easily handle others. The No. 14-seeded Ivanovic ended Williams' bid for a sixth Australian and 18th Grand Slam title with  this prestigious win that took the hottest of favourites out of contention at Melbourne Park and opened up one side of the women's draw.