SOCHI, Russia - Lewis Hamilton just can't catch a break, and it's left him feeling helpless.

Going into the fourth race of the season in Russia, the defending Formula One champion wanted to stage a comeback after already dropping 36 points behind his teammate Nico Rosberg.

Now Sunday's Russian Grand Prix will be all about damage limitation after a power unit problem struck in Saturday's qualifying, leaving Hamilton 10th on the grid.

While Rosberg has cruised to three straight wins, Hamilton's season has been dominated by factors largely beyond his control. The same mysterious failure sent him to the back of the grid at the last race in China, while first-corner contact dropped him back down the field, putting victory out of reach, in the first two races.

"You're almost helpless at some points," Hamilton said Saturday. "The goal is moving further and further away in the distance and I'm doing everything I can do."

It's especially bitter for Hamilton after Mercedes' extreme reliability in pre-season testing while competitors were stuck in the garage.

"We did 800 kilometres (497 miles) a day in testing and the car was faultless," he said. "Then all of a sudden, two times in a row, the same thing. That doesn't happen for us."

Hamilton has won both previous races in Russia, but a third looks out of reach. Sochi's semi-street circuit layout means he will struggle to pass the eight slower cars separating him from Rosberg. To win at the Olympic Park from 10th would be an Olympian feat, and not just because of Hamilton's problems.

Rosberg has shown genuine pace all weekend and was a half-second clear of his British teammate early in the second session with a blistering lap time. With Hamilton 10th and Ferrari's Sebastian Vettel dropped to seventh by a penalty, Sunday's race is his to lose.

Rosberg's win in China was the 17th of his career, the record for most victories in F1 without a championship title, and he knows how car trouble can derail a title challenge.

Back in the summer of 2014, he held a 29-point lead over Hamilton after a collision in Belgium which left bad blood between the pair. However, technical problems forced him out of the race in Singapore and out of the top 10 at the double-points title decider in Abu Dhabi as Hamilton took the championship.

Winning while his main challenger struggles isn't as satisfying as it could be, Rosberg says.

"If Lewis was out there today and I beat him by a couple of tenths, I would be ecstatic because the direct battle brings out these extra-intense emotions," he said.

Rosberg also expects his fair share of car issues this season.

"I can't see into the future," he said. "Normally over a season, especially over 21 races, in F1 things are always evened out at the end of the year."

Meanwhile, Hamilton certainly isn't giving up on his title bid.

Ahead of another race likely to drop him even further back in the title standings, he talked of overcoming "darker days" in his career. "There's always some light there and as long as you focus on that, there'll be a brighter day up ahead."