MELBOURNE -- Former world number one Ana Ivanovic reversed a career-long loss streak against Serena Williams to send the top seed out in the fourth round of the Australian Open 4-6, 6-3, 6-3 on Sunday.
Five-time champion Williams, who had beaten the Serb in all four of their previous matches without dropping a set, was well off the boil in her movements.
The American hinted at carrying a back injury. "I made a tremendous amount of errors. I missed shots I've not missed since the 1980s. I made a lot of unforced errors.
"I'm disappointed to lose today but it's almost good that I lost and I now know what to work on when I get on the practice court. I tried to do the best I could. Maybe I wasn't the best physically, but she did what it takes to win."
Ivanovic lost the opening set for her ninth on the trot against Williams before turning on the afterburners to pave the way for the win in a shade under two hours.
The Melbourne favourite, with relatives in the city, next plays the winner from Canadian Eugenie Bouchard and Australian Casey Dellacqua.
Williams went down for only the second time in Australia after winning a first set, with the loss her second from 53 matches played.
The 2008 French Open winner Ivanovic could not have been more pleased.
"It's amazing, honestly, I just went out to play as best I could. I played really well, I'm so thrilled," said the winner who broke on four of 14 chances.
"I played very consistently, it's not easy to play such a champion, But she's just a human and has the same pressures as anyone else. I went out swinging at the ball and did that really well."
China's fourth seed Li Na, losing finalist last year, advanced over Russian Ekaterina Makarova 6-2, 6-0 while Italian veteran Flavia Pennetta upset German ninth seed Angelique Kerber 6-1, 4-6, 7-5.
Williams stood 77-3 since last year's Australian Open and came to court against Ivanovic after having won a record 61st Melbourne match. The Ivanovic match was here 70th at the tournament, another record.
Ivanovic has now reached the quarter=finals of a major for only the second time (2012 US Open) since winning Roland Garros and taking over the top ranking six years ago.
Swiss-based Pennetta, who turns 32 next month, reached a Melbourne quarter-final for the first time with her win over Kerber, losing finalist last weekend in Sydney.
She was playing after injuring a wrist at the Hopman Cup at the start of the month and only got a late go-ahead from doctors after no serious damage was found in a scan.
"It's amazing, it's always nice to be in the quarter-final of a grand slam. Today was a really good match. I'm here and trying to play my best tennis, trying to enjoy every moment."
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