For 2017 Ford Fusion Energi, here is the quote from owner's manual page 154.
"For best overall vehicle and engine performance, premium fuel with an octane rating of 91 or higher is recommended."
Octane rating 87 is the MINIMUM requirement.
For the first fill up, I used Octane 87 fuel, and I felt my car was not as smooth and responsive as the tester car, and the tester car only has 25 km (both cars were 2017 Ford Fusion Titanium trim). On the second fill up, I used Octane 93, and the gas engine was running smoother and more responsive.
I will stick with Octane 93, since I only fill up the tank once every 2-3 month. Using 87 octane rating won't harm the car, you have a choice.