SOCHI, Russia (Reuters) - Ferrari are still waiting to take the fight to Formula One champions Mercedes after a Russian Grand Prix that left even their dominant rivals surprised by the gap in performance.

Mercedes F1 driver Nico Rosberg of Germany (C) jumps on the podium as he celebrates victory during the Russian Grand Prix. REUTERS/Maxim Shemetov

“We’ve always said that they’ve been close but this weekend they were not close at all,” Mercedes winner and championship leader Nico Rosberg told reporters after his seventh win in succession on Sunday.

“We were really far ahead this weekend and that’s been impressive to see.”

Rosberg said the unique characteristics of the Sochi asphalt might have accounted for some of the advantage but Ferrari team principal Maurizio Arrivabene was not looking for excuses.

His post-race telephone conversation with hard-minded company president Sergio Marchionne was not going to give him any pleasure either.

“For sure he is not going to be amused,” said the Italian.

Even bad luck, with four-times world champion Sebastian Vettel taken out at the start when Red Bull’s Russian Daniil Kvyat twice drove into the back of him, could not hide the failings.

Vettel was seventh on the grid, and next to Kvyat, only because of a penalty for an earlier gearbox failure and replacement.

Kimi Raikkonen, who took Ferrari’s 700th grand prix podium, finished third but 31 seconds behind Rosberg who had already turned down his power unit and had no need to push.

“On the Sochi circuit yes, I was surprised,” said Arrivabene. “Believe me: I don’t want this to happen again.

“I don’t think things can be explained as bad luck, there are mostly human mistakes behind the story.”

Arrivabene said Ferrari had to improve reliability. He felt sure, however, that the car had yet to show its true potential and the combination of more favorable tracks and engine tweaks would help.

Raikkonen agreed, even if the task was formidable with Mercedes having won the last 10 races and 36 out of 42 since the start of 2014.

“We know quite a few small things that we want to improve, and we know that there’s some improvements coming,” said the Finn. “But Mercedes were very fast for the last few years and they are fast this year.

“I don’t think that so far this year we have ever really put together a really clean weekend either so that doesn’t help,” he added.

“You cannot give anything away and expect to beat a team like them... we are behind where we want to be but I’m sure as a team we will get there.”