Next week: Navratilova def. Serena 6-4, 4-0 ret.
It will happen.
Navratilova is winning grandslams and titles in doubles right now, she's also used to returning big serves in mixed doubles, she even recently beat Monica in an exhibition. Yeah Monica was not in top form but still, it's a nice win.
Also, add the fact that the clay will slow down Serena's serve and groundstrokes, that it will give more time for Navratilova to get to the balls, and the most important fact which is that Navratilova has all the shots in the game and could drive Serena crazy with her drop shots, relentless net attacks (something that Serena has never faced), slice shots, top spin, variety, add also the fact that Navratilova has a lot of experience. And there you have it, a Navratilova win.