Sebastian Vettel expects Mercedes to come roaring back on Saturday after a subdued time in Friday's practice.
Vettel and his Ferrari team mate Kimi Raikkonen were comfortably ahead the first two free practice sessions. But Vettel believed that Mercedes were just playing things close to their chest.
"I think they will be fine; it's a circuit that suits them, so they will be strong tomorrow," he predicted.
"Last year people expected Williams to be fastest after the Friday, if I remember right," he pointed out. "It obviously turned out that Mercedes was the fastest. That's how sometimes you can be misled.
"I think there are a lot of things that we can play with in the car - fuel loads, engines, engine modes. This track, especially, there are a lot of things that you can show or not show.
"I think the most important step is we talk about ourselves, our balance, and as I said I was able to improve, so I'm reasonably happy."
While Vettel set the fastest time of the day in the afternoon, Raikkonen had been on top in the morning session.
"It's been quite a nice Friday, things have been running smoothly," said the Finn. "I'm happy with the car so it's more fun right now.
"It's only Friday, we have no idea what the others are doing, but so far we've started well. Quite happy out in front today, so we have to try to make a good day tomorrow and then go from there.
"Tomorrow's another day."
GALLERY: All the pictures from Friday in Sochi
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