Muguruza leads their previous matches 3-1. Their last meeting was in February this year. That was on an indoor hard court and Muguruza won in straight sets. She won their last 3. Jankovic’s win was on clay in 2013. She won in straight sets.
Both have struggled at times on hard courts this year though Muguruza has a slight edge. She often loses sets when she should be winning in 2 sets. There is a chance that this also goes to a deciding set but I would favour Muguruza to win.
I may wait for JJ to win set 1 before backing Muguruza.