Ferrari has played down claims it is the obvious favourite to win in Baku.
After China, the famous team returned to its Maranello base and worked on a new rear wing and aerodynamic package that produces more downforce for Baku.
Sebastian Vettel and Charles Leclerc then dominated Friday practice with a car that is now fast on the corners as well as the straights.
"It's about time," said Vettel.
Mercedes' Lewis Hamilton commented: "We'll do everything we can, but it is unlikely that we will find seven tenths overnight.
"It looks like they are a long way ahead of us."
However, Leclerc said he is "sure" Mercedes will bounce back.
"We are fast," he said, "but tomorrow Mercedes will be faster than they were. I'm sure of it," he said.
"They were very fast on the long runs, so there is no reason they would be slow on a fast lap too. Tomorrow we are in for a very close fight."
Vettel agrees that Mercedes will be faster on Saturday than the team was on Friday.
"I think we showed a little bit more than they did," the German was quoted by RTL after Friday practice. "Mercedes are the ones to beat."
