I can see Safarova drifting below evens closer to match starting time. They haven't met before, so one can't figure out match-ups but I can think of couple things to make a case for Lucie here.
First of all, experience. At this stage of the tournament it's all about who has been there before. Safarova has gone past QF at major, doing so at Wimbledon last year. Muguruza has not. She played good first set against Sharapova last year before fading.
Secondly, my problem with Muguruza is that she tends to make way too many unforced errors. She was down a break in both sets against Pennetta in previous round but managed to come back and win 2-0. It won't work against Lucie because Safarova has better serve than Flavia has got.
For me , Safarova is favorite in this game.