Sebastian Vettel said it was a "no-brainer" for Mercedes to move Valtteri Bottas aside for his championship rival Lewis Hamilton in the Russian Grand Prix.

Ferrari driver Vettel is facing an almost impossible task of stopping Hamilton from galloping towards a fifth world title after the Briton extended his lead to 50 points.

Indeed, Hamilton can now afford to finish second at the concluding five rounds, and still win the championship.

Mercedes courted criticism for manufacturing the 70th win of Hamilton's career, but Vettel defended their controversial decision.

"Lewis and Valtteri played the game together as a team very well," he said. "In the position they are in, what Mercedes did today was a no-brainer."

The Sochi Autodrom was expected to suit Ferrari's package over Mercedes', but despite bringing a heavily-revised car to the Black Sea coast, the Italian team were no match for their rivals.

Vettel qualified a distant third, and despite managing to leapfrog Hamilton during the only round of tyre stops, he was unable to keep the Mercedes car at bay.

For the first time this year, the championship is now out of Vettel's hands, and the German admitted he is running out of time to stop Hamilton.

"I wasn't a genius in maths, but I was clever enough to pay attention and realise that it isn't getting easier if we lose points," he added.

"We tried our maximum and there was a slim chance to finish ahead of Lewis, but we have to be happy with third and settle for that.

"I still believe in our chance. Yes, it is not getting bigger, but who knows? It takes one DNF, and then all of a sudden things look different.

"So, we need to stay at the top of our game and make sure we focus on winning the last races."