Sebastian Vettel has insisted that the 2016 title race is not already over.

Many think that Nico Rosberg, who could extend his extraordinary winning streak from six to seven straight races in Russia, is now pulling into an unassailable position at the top of the drivers' world championship.

It comes amid an almost equally extraordinary run of bad luck for Rosberg's Mercedes teammate, the reigning champion Lewis Hamilton, who starts just 10th at Sochi after an identical engine problem to the one he suffered two weeks ago.

"The same problem twice must not happen," team chairman Niki Lauda said on Saturday. "I need to talk to Andy," he added, referring to Mercedes engine chief Andy Cowell.

Ferrari's Vettel, on the other hand, was the best part of a second in pace behind Rosberg in qualifying, while a gearbox change means that he takes a grid drop for Sunday.

On the reliability problems, Ferrari team boss Maurizio Arrivabene has admitted that the Maranello team has been "pushing like crazy" to catch Mercedes.

"We are risking a lot," he told Italy's Sky in Russia. "Maybe too much, and that's my fault."

Vettel, however, told the same broadcaster that he is sure Ferrari is not out of the running yet.

"We have not won [races] yet, but we will. We will fight for the championship, I'm sure," said the German.

"I don't think anyone would say that, after only three races, we are out of it."

The Russian Grand Prix gets underway at 1pm BST.