Melbourne, Australia • For almost a year, Serena Williams won professional tennis matches at an improbable 96 percent clip. Since her exit from the 2013 Australian Open, she had played 80 matches and had won 77 of them.
As her fourth-round contest in this Australian Open wore on, though, Williams looked less and less like the most dominant player in women’s tennis. She was undone by a flurry of botched backhands, back pain and an opponent, Ana Ivanovic, who played more like a current world No. 1 than a former world No. 1.
The crowd, squarely against Williams, rose to its feet and roared at the biggest upset so far in this tournament when the match ended with Ivanovic the winner, 4-6, 6-3, 6-3. Williams smiled as she shook her opponent’s hand. Ivanovic had never beaten her — until Sunday.
“It’s amazing,” Ivanovic said in her television interview on court. “I just played really well.”
Over the first week of the Australian Open, Williams had accumulated records. She set the mark for most match wins in women’s singles at this tournament (61) and most women’s singles matches played (70).
All the while, she sought an even bigger milestone: an 18th Grand Slam singles championship. That would have put Williams in rare company, tied with Chris Evert and Martina Navratilova for second-most in history, within sight of Steffi Graf and her historic 22 titles.
Instead, other numbers surfaced in defeat. Like this one: In a career filled with Grand Slam tournaments, Williams had won the first set and still lost five times in a career that started in 1995.
“I made a tremendous amount of errors,” Williams said at her post-match news conference. “Shots I missed that I normally don’t miss.”
Williams tried to play down her physical problems, and said she wouldn’t make excuses. However, she added: “I obviously wasn’t hitting the way I normally would hit. Or moving the way I normally would move.”
Williams cruised through the first three rounds of this Australian Open. She blew off one scheduled on-court interview after her third-round victory and offered an oblique explanation that she was busy and other tasks awaited. She confirmed after Sunday’s match that she was having back pain.
Whatever the reason, she looked off on Sunday, even as she fought through and took the first set. She did not bend well on the backhand side, and she did not move well, and after she missed a return early in the second set she bent over in apparent pain.
Ivanovic capitalized. Since she won the French Open in 2008, Ivanovic had mostly disappointed. Her last run to a Grand Slam quarterfinal came at the U.S. Open in 2012.
On Sunday, she blitzed Williams from the baseline, matched Williams for serve efficiency and showcased a varied game that kept Williams on the defensive more than usual. Ivanovic dictated how the match unfolded.
On the big points that Williams won, she often screamed loudly or pumped her fist emphatically. She stole repeated glances at her box and walked gingerly between points.
Williams said she almost pulled out, adding, “I mean, I probably should have.”
She gave credit to Ivanovic and said: “It’s not like I gave her the match. I tried to fight the best I could today.”
With Williams’ defeat, which ended a 25-match winning streak, the women’s singles draw has opened significantly. Ivanovic, seeded 14th, joined Li Na (4) and Flavia Pennetta (28) as Sunday winners now into the quarterfinals.
Li, a two-time finalist, needed only 59 minutes to register a 6-2, 6-0 win over Ekaterina Makarova. Li broke No. 22 Marakova’s serve five times. In the next round, Li will play Pennetta, who beat No. 9 Angelique Kerber, 6-1, 4-6, 7-5.
O Ana Ivanovic defeats Serena Williams 4-6, 6-3, 6-3, ending Williams’ 25-match winning streak.
• Two-time finalist Li Na beats Ekaterina Makarova 6-2, 6-0.
• No. 28 Flavia Pennetta upsets No. 9 Angelique Kerber 6-1, 4-6, 7-5.