MELBOURNE, Australia — Serena Williams' long winning streak came to an end in an upset 4-6, 6-3, 6-3 loss to Ana Ivanovic today in the fourth round of the Australian Open.
"It's amazing," Ivanovic said. "Honestly, I went on the court and I just wanted to play the best I could. I'm so thrilled."
Williams, the world No. 1, hadn't lost a match since August, which was one of only four defeats in 2013, and she came into the fourth round with 25 straight wins. It was her 70th match at Melbourne Park, a record in the Open era, and she set the mark for match wins ever at the Australian Open with her third-round victory.
Williams, 32, was well short of her best at Rod Laver Arena. After the match, she acknowledged she was battling a back injury and had considered pulling out of the tournament, though she stressed several times that that wasn't the reason she lost and credited Ivanovic's play.
Ivanovic hadn't taken a set off Williams in their previous four matches. Since her French Open win in 2008, the former world No. 1 has not even reached a Grand Slam semifinal. This is only her second quarterfinal in a Slam since then (2012 U.S. Open).
The Serb was able to threaten Williams' usually impregnable serve from the outset. She fashioned four break points in the opening set, converting one, but was broken twice as Williams edged it out.
Ivanovic took over from that point, her once fragile serve holding up well as Williams appeared to struggle with her movement, and she did not face another break point.
Williams was warned for a time violation when serving to stay in the match and managed to save two match points, but Ivanovic closed it out with a love hold after 1 hour and 56 minutes.
"I was very consistent," Ivanovic said. "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."
The other quarterfinal features two women who turn 32 next month, with two-time finalist Li Na wrapping up a fourth-round win over No. 22 Ekaterina Makarova in less than an hour to set up a match against Flavia Pennetta.
The 2011 French Open champion broke Makarova's serve five times and fended off four break points on her own serve during a 59-minute, 6-2, 6-0 win to reach the quarterfinals here for the fourth time in five years.
Pennetta's late-career revival continued as she reached her first Australian quarterfinal with a 6-1, 4-6, 7-5 win over ninth-seeded Angelique Kerber of Germany.
The 28th-seeded Pennetta has played some of her best tennis since returning last February from a wrist injury that caused her ranking to drop as low as No. 166.
On the men's side, three-time defending champion Novak Djokovic was set to take on Italian Fabio Fognini for a place in the quarterfinals. Djokovic was attempting to make his 19th consecutive appearance in the quarterfinals of a Grand Slam.