Lewis Hamilton believes that Mercedes has strong pace around the streets of Sochi but remains wary of the potential of rivals Ferrari.
Hamilton led the way during the second practice session at a venue where he has emerged victorious on both of Formula 1's visits.
Hamilton finished over seven-tenths clear of Ferrari's Sebastian Vettel, who encountered an electrical issue, but remains cautious regarding the potential of Mercedes' rivals.
"It's been a constructive day to start the weekend," he said. "We got through most of our programme except one last little bit at the end as some of my tyres were flat-spotted but no big drama there.
"I think we're looking strong here - but we need to keep working hard if we are to try and stay ahead of the Ferraris. They look like they might be another step closer this weekend.
"We've got a few things to look at to make sure we perfect the setup for qualifying, so we shall see how it goes."
Championship leader Nico Rosberg finished third after failing to nail a lap on the Super Soft tyres.
"It's difficult to get it right at this track, as there's only a small window where the tyres work perfectly and a lot of places where you can easily make mistakes," he said.
"I didn't manage to hook up a full quick lap on the SuperSoft in FP2. But, aside from that, it was a good day. The car felt good on a quick lap this morning and again on the longer runs this afternoon, so that's very encouraging."