Lewis Hamilton admitted that he and Mercedes have a battle on their hands and will have to find a solution to their problems in Sunday's Russian Grand Prix.
The three-time world champion qualified down in fourth behind pole-sitter Sebastian Vettel and his Ferrari team-mate Kimi Raikkonen in Saturday's qualifying session, with his own Mercedes team-mate Valtteri Bottas lining up third.
It was Ferrari's first front row lock out since 2008 and ended champions Mercedes run of 18 pole positions.
"I just wasn't quick enough today," said Hamilton. "I think we have to go back to the drawing board and try and figure out why. Tomorrow it's still all to play for.
"I'm still up there in the mix. It was all in the last sector -- I was losing half a second. So, there's some work to do. That's where all the mistakes happen.
"It was a real struggle, getting tyre temperature and really maximising and utilising the tyres.
"It was an issue yesterday and we made some changes and it worked, but then too much, maybe, because that last sector was a struggle."
The Briton, who lies seven points behind four-time champion Vettel in the championship this year after three races, added he expected a "real race" on Sunday.
"Ferrari are quickest here today and generally during race trim runs so it'll be interesting to see where we stand," he said.