By Alan Baldwin
SOCHI, Russia (Reuters) - Formula One frontrunner Sebastian Vettel led a Ferrari one-two in Russian Grand Prix practice on Friday with the resurgent Italian team appearing to have a clear edge over champions Mercedes.
The German four-times world champion enjoyed the afternoon sunshine with a best lap of one minute 34.120 seconds -- 0.263 quicker than team mate Kimi Raikkonen and 0.709 clear of Mercedes' Lewis Hamilton.
Raikkonen had been fastest in the morning.
Valtteri Bottas, a close second in opening practice, was third in the afternoon for Mercedes and 0.670 off Vettel's pace, while team mate Hamilton was fourth.
Vettel leads Hamilton by seven points after winning two of three races this season. The Briton won in China.
Sochi's street circuit, winding around the landmark venues of the 2014 Olympic Park, has favoured Mercedes since its debut three years ago with the champions leading every lap of every race there.
Triple champion Hamilton won in 2014 and 2015 with now-retired team mate Nico Rosberg triumphant last year on his way to the title.
"This is a circuit that suits them," commented Vettel, despite mounting evidence that the three-year Silver Arrows' domination is on the wane. "They will be strong tomorrow."
Raikkonen and Bottas also have good records in Sochi, however, with the 2007 world champion finishing third last year and his fellow-Finn taking the first fastest lap of his Formula One career in 2014 when he also came third for Williams.
Vettel was second in Russia in 2015.
"As a team I think we've come a long way from the last few years," Raikkonen had told reporters on Thursday.
"Are we at the same level as them (Mercedes)? I don’t know. It's not far off, let's put it that way."
The morning session was halted briefly when the engine cover blew off Esteban Ocon's Force India, leaving debris for marshals to recover.
Russian reserve Sergey Sirotkin replaced Germany's Nico Hulkenberg at Renault for the opening session but the car broke down on track before he could do a timed lap and was pushed off by marshals.
Red Bull's Max Verstappen had problems in the afternoon, pulling over and complaining of a lack of power, while McLaren again struggled with Belgian rookie Stoffel Vandoorne already resigned to starting the race at the back after an engine change.
(Reporting by Alan Baldwin, editing by Mitch Phillips)