Vika was all but down and out, incl. a MP to Knapp, but she gutted it out and won the TB, so onto a 3rd set. Not sure what goes on with her knee. Not taped.
So Vika retires and will head home early.
I really sort of hate this trope that some players are "made out of glass." It's sports, and people get injured. Some more than others. But injury is a usual side-effect of sports.azarenka keeps getting injured. she is made out of glass.