BRISBANE, Australia -- Serena Williams retired during the second set of her Hopman Cup match in Perth on Tuesday, completing a day of injuries and upsets for the leading players on the women's tour less than two weeks from the Australian Open.
Williams, who missed the U.S. team's opening loss to Ukraine on Monday because of inflammation in her left knee, trailed 7-5, 2-1 against Jarmila Wolfe when she left the court in her first match of the season.
"I just have some inflammation that's been going away very slowly,'' Williams said. "It's going away, but just needs a little more time.
"I've been training really hard during the offseason. Really pushing myself beyond the limits. I just think a day off or two will make a world of difference.''
Other top 10 women joined Williams on the injured list. At the Brisbane International, defending champion Maria Sharapova and top-seeded Simona Halep withdrew because of injuries within an hour of each other, without playing a match. At the ASB Classic in Auckland, New Zealand, defending champion Venus Williams and 2014 winner Ana Ivanovic were ousted in first-round upsets.