Mercedes boss Toto Wolff insists that his team wasn't 'sandbagging' during Friday's practice sessions at Sochi.
Ferrari opened up a big gap at the top of the timesheets over their rivals. Wolff admitted this was a genuine snapshot of the different performance levels between the two teams.
"The Ferrari was extremely quick throughout the session, on one lap and the long run was impressive," Wolff admitted to Sky Sports F1.
"There's a bit of work to do," he added.
Even so, Wolff isn't ruling out the possibility that Mercedes had simply been using the track time differently to their rivals.
"Everybody's doing a bit of a weird programme sometimes to find out where they are," he acknowledged.
Wolff said Friday's result demonstrated that Mercedes could no longer take its superiority for granted following the introduction of new technical regulations over the winter.
"We've said it before - it's all new [in 2017]. We've been very good on the track in the last couple of years, but it's all changed.
"The cars have much more downforce. The tyres are completely different. You cannot anticipate that it's going to continue."
"We have this discussion sometimes on the Friday," he continued. "I remember it was Melbourne or Shanghai. We'd been a second faster on the long runs [on Friday] than everybody else, and it just changed on Saturday and Sunday.
Mercedes had a 'painful' time in the last Grand Prix in Bahrain, but Wolff said there was little in common between Sakhir and Sochi.
"We had an overheating of the tyre [in Bahrain]," he said. "It was very hard to explore how we would handle the tyre in very hot conditions going forward.
"This is very different here. It's a very smooth track, it's not very hot, so there's not a lot you can translate from Bahrain to here."
GALLERY: All the pictures from Friday in Sochi
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