MELBOURNE, Australia (AP) - Moments before she started pounding the first of her many winners past Serena Williams at the Australian Open, Ana Ivanovic listened intently to the announcer on Rod Laver Arena outlining the extraordinary accomplishments of the woman soon to be across the net from her.
Williams, a five-time champion at Melbourne Park, won 78 of her 82 matches in 2013, and was coming into the fourth round on the second-longest winning streak of her career - 25 matches.
It was her 70th match at the Australian Open, a record in the Open Era. And then, of course, there's the 17 major singles championships.
"When we were starting the match and they were talking about all her Grand Slam titles, it was quite impressive," Ivanovic said, recalling the pre-match introductions. "But I didn't think much about the occasion and who I was playing, because it can get overwhelming."
True to her word, Ivanovic, who had never won a set against Williams in four previous meetings, took on the biggest serve in women's tennis without fear. And she hit pinpoint forehands - 20 of 33 winners were on that side - to all areas of the court. Williams, who later revealed she was carrying a back injury, didn't even bother trying to chase some of them down.
Just under two hours later, it was game, set and match: 4-6, 6-3, 6-3 and an upset victory to put Ivanovic into the quarterfinals of the Australian Open for the first time since her run to the final in 2008.
"It's not easy playing such a champion ... but she is also just a human," said Ivanovic. "I just went out there swinging."
Williams never got into the swing of things, at least not to way Ivanovic expected. She noticed from the outset that Williams' serve seemed to lack its usual zip. Williams also made some very uncharacteristic errors on her backhand, a telltale sign of back pain.
"It wasn't the best," Williams admitted later, sounding surprised when asked about the back injury. Her coach had let it slip after the players walked off the court that Williams had been experiencing back pain for days.
"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."
Ivanovic will next play 19-year-old Canadian Eugenie Bouchard, who had a 6-7 (5), 6-2, 6-0 win over local hope Casey Dellacqua.
The other quarterfinal in Ivanovic's half will feature two-time finalist Li Na, who beat No. 22 Ekaterina Makarova 6-2, 6-0, and No. 28 Flavia Pennetta, who defeated No. 9 Angelique Kerber 6-1, 4-6, 7-5.
The men's draw progressed more according to rankings when three-time defending champion Novak Djokovic and No. 3 David Ferrer advanced to the quarterfinals, along with No. 7 Tomas Berdych and No. 8 Stanislas Wawrinka.
Djokovic continued his bid for a fourth straight Australian title with a 6-3, 6-0, 6-2 win over Fabio Fognini. Ferrer beat Florian Mayer 6-7 (5), 7-5, 6-2, 6-1 and will next play Berdych, the 2010 Wimbledon finalist.
Djokovic will play Wawrinka, who finished off the Sunday night program at Rod Laver with a 6-3, 7-6 (3), 7-6 (5) win over Tommy Robredo.
"I've been elevating my game as the tournament is going on," said Djokovic, who later entertained the crowd with an impersonation of his new coach, Boris Becker. "The general feeling on the court, all the shots, using the court position really well, being aggressive, playing my style of the game."
On Monday, Djokovic's major threats to the title - top-seeded Rafael Nadal, Wimbledon champion Andy Murray and 17-time Grand Slam singles winner Roger Federer - will play their fourth-round matches. Two-time defending champion Victoria Azarenka and No. 3 Maria Sharapova are in action on the women's side.
Ivanovic will have the day off - she's planning a celebratory dinner with some of her Serbian relatives who live in Melbourne.
Asked if having Williams out of any Grand Slam makes a difference, Ivanovic said it "definitely" did, then explained why in effusive terms.
"I think she's done so much for the sport, and she's still doing it," Ivanovic said. "She's such a great athlete and a great person to have on tour. We want her, because it pushes us."
With the challenge met on Sunday, Ivanovic, at the urging of several fans, attempted to throw a souvenir towel into the stands. The breeze blew it back at her.
She was plainly off the mark, perhaps for the only time all day.