@margo,
As does Serena Williams, Kiki Bertens and Garbine Muguruza. You never know which Stosur is going to turn up at any given tournament. She could be the world beater who beat the daylights out of Williams in 2011 US Open or the first round loser that shows up the Australian Open on occasion. Muguruza is the real deal though, so Stosur better be feeling it tomorrow.