Serena Williams is out. Petrova beat her: 6-2 and 6-3.
Afterwards Serena admitted that her meft knee troubled her during the game.
That's what I was afraid of, she took this way too lightly after such a serious operation. Her first couple of matches were no problem, but I was more worried about a long string of consecutive matches, what effect that would have on her healed knee ... I was obviously more worried about it, than she seemed to be.
I think it will still take some time before the old routine gets back in that knee ...