As Hamilton toiled to only fourth, his new Mercedes team-mate Valtteri Bottas clinched the first victory of his Formula One career at the 81st attempt as he became the third winner in just four races of this unpredictable season.
Bottas held his nerve in a nail-biting ending at the Sochi Autodrome - with Vettel crossing the line just 0.6 seconds behind the Finnish driver - to move to within 10 points of Hamilton, and in doing so, firmly throw his crash helmet into the championship ring.
But as Bottas mastered the race from the outset - after leaping from third to first in the 220mph drag down to turn two - a perplexed Hamilton could not keep pace with the leading trio.
He has been mysteriously off colour all weekend and struggled for balance throughout Sunday’s race. Hamilton, who also bemoaned an overheating engine in a number of fractious radio messages.
“I can’t explain it right now, but we will do some work over this week to fully understand it,” Hamilton said.
For Bottas, he arrived at the fourth round of the championship facing question marks over his position at Mercedes after he was ordered out of Hamilton’s way in Bahrain.
But the 27-year-old, who was plucked from Williams to fill Rosberg’s championship-winning seat only in January, responded in exemplary fashion and must now be considered as a real threat, not only to Hamilton and his de facto number one status at Mercedes, but perhaps Vettel, for this year’s title, too.
“For me winning the championship is the only goal in my career so we will keep pushing for that,”
Bottas, who received his winner’s trophy from Russian President Vladimir Putin, said. “I am not that emotional but hearing the Finnish national anthem is something quite special.
“It took quite a while to win - more than 80 races for me - but it was definitely worth the wait. This strange opportunity came to me in the winter to join this team.”
It was a day to forget for Hamilton and yet another one for Fernando Alonso and his red-faced McLaren team. The double world champion did not even make it to the startfter he parked his car at the entry to the pit lane on the formation lap following a failure with his Honda engine.
Kimi Raikkonen completed the podium places for Ferrari, with Red Bull’s Max Verstappen fifth and the Force India of Sergio Perez sixth.