MELBOURNE, Jan. 19 -- Women's top seed and world's No.1 player Serena Williams was beaten by Serbia's 14th-seeded Ana Ivanovic for the first time here on Sunday in the fourth-round of the Australian Open.

Williams, who was also the top seed in 2013, was eliminated by 19-year-old-then fellow American Sloane Stephens in last year's quarterfinals, which was the biggest upset of the tournament as Stephens reached her career first Grand Slam semifinals.

Williams returned with more power to the Melbourne Park as she went 78-4, won 11 titles and became the oldest player to ever rank No.1, all in 2013.

Williams dominated the previous four meetings against Ivanovic and never let the Serbian even won a set off. Williams won the first set 6-5 and made the match look like another stride to the quarterfinals for the five-time champion.

It was the second set that turned things. Ivanovic hit 15 winners and dominated with her first serve. Williams struggled with her first serve for most of the match and Ivanovic pounced on every second serve to give herself the advantage in points.

"I made a tremendous amount of errors and I missed shots I normally don't miss. Shots I haven't missed since the '80s." said Williams. "I definitely didn't feel myself today."

"Serena is such a great player. Going on to the court today, I really just tried to give my best. I tried to make it a good match." said Ivanovic. "I was very competitive till the last moment, and I'm just very thrilled, obviously."

Ivanovic reached the final here six years ago but lost to Maria Sharapova. But she then won at Roland Garros. In the last five years her ranking sticking largely between 10 and 25.

Ivanovic will play against the winner between Aussis wildcard Casey Dellacqua and Canadian Eugenie Bouchard in Tuesday's quarterfinals.