Verstappen was second-fastest in the day's latter session, held under night skies, but struggled in the opening hour of running.
Held in the sunshine, conditions in which neither qualifying nor the race will be held, the Dutchman was unable to replicate the pace he'd enjoyed during pre-season testing a week ago.
“Difficult start to the day,” he confessed.
“I mean, FP1 was really bad, just couldn't get a balance which was a bit odd because in testing, whatever we tried, okay, some things were maybe not amazing, but not that far out.
“So, a few things to understand.”Even the start of FP2 was a bit difficult, but then I think for the final run, even though not really having a good reference and confidence up until then in the car, the last was not too bad.
“Also the car felt a bit more connected.”
Aston Martin challenge
The Silverstone-based squad enjoyed a promising pre-season test, with impressive long-run pace in particular.
“You could see that already in testing they were very competitive,” said Verstappen of Aston Martin's pace.
“They had a great day. For us, still a bit of work to do. We know that we have a very competitive car, it's just now putting all the pieces together.
“Looking at his own pace, Verstappen was satisfied at the fundamentals of the car at his disposal in Bahrain this weekend.
“I think the long run, with all the changes we made, I was quite surprised, the pace we had,” he ventured.
“Overall, the car is not too bad in the long run. I just need to find my rhythm again with the car and just the way the car's driving from short run to long run.
“If I feel happy in the car again, and I can push like I want to push with the car on one lap, then for sure we are very fast,” he added.
“But it's also of course making sure the car doesn't fall out of the window for the long run.”
Another 60 minutes of practice awaits drivers on Saturday, beginning at 14:30 local time (22:30 AEDT) ahead of qualifying.