Russian GP: Lewis Hamilton says he can't fall further behind Nico Rosberg

Nico Rosberg (left) has won all three races of the season so far

Lewis Hamilton says he must beat Mercedes team-mate Nico Rosberg at this weekend's Russian Grand Prix to kick-start his title defence.

Rosberg has won the first three races of the season to build a commanding 36-point lead in the championship.

Hamilton said: "Of course there is an urgency. I can't really afford to fall any further back than that.

"Who knows how the weekend will go? It could be as bad as in the past, but I'm hoping it will be positive."

Hamilton, a triple world champion who has won the last two titles, has finished second, third and seventh in the races so far.

Bad starts took him out of the reckoning for victory in the first two races in Australia and Bahrain before technical trouble in China left him at the back of the grid.

Lewis Hamilton's car's aerodynamics were damaged when he was hit by a Sauber on the first lap in China

Formula 1 has introduced new rules this season that gives the drivers more control at starts, reducing the technical assistance they get from the car.

Hamilton said he had been encouraged by the fact he had made a good start in Shanghai from his position at the back of the grid.

"At the end of the weekend, the team analyse the starts and I had the best of everyone," claimed the Englishman.

"This is a circuit where you need that because I think it is one of the longest runs to Turn One and it is easy to get drafted so a good start would help."

Rosberg, who has won won six grands prix in a row dating back to last October in Mexico, said he was expecting a fightback from Hamilton.

"I'm pleased with the way I'm driving," said the German.

"I have been driving really well, but my opposition had a really messy start and I definitely expect them to bounce back, especially Lewis."

Rosberg said Ferrari would also be a tough challenge for Mercedes, despite their difficult start to the season.

"I'm not sounding a note of caution, I'm just realistic," he added.

"Ferrari, among others, haven't shown what they can do yet. They are a lot quicker than they have shown and for sure they are very close to us."

Ferrari driver Sebastian Vettel said he believed the Italian team were still not quite on the pace of the Mercedes.

"I hope we can be very close this weekend," the four-time champion said. "First of all, have a smooth weekend and see where we are.

"We know we are probably not close enough, but the race is on Sunday and there is always a chance."