Serena Advances After Ill Azarenka Retires

Azarenka was leading 6-3 2-4 when the 13th seed was forced to retire as the effects of the virus sapped her energy completely.

Serena Williams was gifted a place in the quarter-finals of the Australian Open on Monday when the American's fourth-round opponent Victoria Azarenka succumbed to a mystery virus.

Azarenka, from Belarus, was leading 6-3 2-4 when the 13th seed was forced to retire as the effects of the virus sapped her energy completely.

The 19-year-old almost fainted as she started feeling dizzy and struggled to maintain her balance.

She took a medical break after almost vomiting into her hands and tried to keep out of the sun by stumbling into the shade at the end of each point.

"I started feeling really sick in the morning, I woke up at 6 a.m. and I was throwing up all morning. I just felt so weak," Azarenka told reporters.

"Once I got to the court, I went to see the doctor, I felt a little bit better. Throughout the first set, a little bit of the second, then I just had no more energy to go."

Azarenka said she was told not to continue after her medical time-out but wanted to give it one last shot.

When she eventually retired, she hobbled to the net to shake hands with second seed Williams then needed two assistants to help her walk off court.

"I was trying to keep going as much as possible but there was nothing you can do. (If I took one more step) I would fall over," she said.

"It was disappointing for me that I played that well and I couldn't handle a little bit more... but, whatever happens, happens. I just have to accept that."

WILLIAMS WORRIED

Williams said she also became concerned about Azarenka's condition in the second set.

"Honestly, I got worried," Williams said.

"I was like, 'Oh, my goodness', because she started walking really slow.

"The last thing she would want to do, to me, would be fall.

"It was just weird. I was actually really worried."

Williams had her own problems during the match, requiring treatment to both ankles, but said she was still always confident of winning.

The American struggled with her serve in the first set and her frustration boiled over and she received a code violation when she screamed out an expletive.

"My serve hasn't been anywhere near where it normally is so I just got a little frustrated with my first serve percentage. It seemed to be low today," she said.

"When I lost the first set, I was thinking automatic three sets.

"There's nothing else. I'm thinking, Okay, this is what I'm going to do in the third. I automatically try to assume I'm going to win the second."

Williams, a three-time winner of the Australian Open, will play Russia's Svetlana Kuznetsova in the quarter-finals after her fourth-round opponent Zheng Jie retired with a wrist injury.

"She's extremely strong. I think we have a similar game. I think it will obviously be a great match," Williams said.

"She's extremely powerful. She just can get a lot of things back, kind of like me."