Valtteri Bottas conceded that Mercedes gap to rivals Ferrari and Red Bull is "bigger than expected " following the opening day of running at the Mexican Grand Prix.
Bottas concluded Friday afternoon's session more than half a second adrift from pace setter Sebastian Vettel who led Red Bull's Max Verstappen and Ferrari teammate Charles Leclerc in FP2.
Mercedes' single-lap pace - or rather its deficit to its rivals - surprised the Finn.
"It's bigger than we expected at this point of the weekend. But it's hopefully not a miracle to find some gains," Bottas said.
"It was pretty slippery today out there, especially the first session was very tricky, with the oversteery balance of the car.
"Felt a lot better in the second practice, actually not a bad feeling, but still I think we were lacking a bit of a grip.
"Both Ferrari and Red Bull seem to be performing well on this track so far, but as always, it's only Friday and there's usually lots of things we can do a little bit better next day, just need to work hard tonight."
Lewis Hamilton enjoyed a productive start to his day, clocking in with the fastest lap in FP1, but the Briton then saw his pace dwindle in the afternoon
"This is how it usually is for us anyways here," said Hamilton who warned in the run-up to the Mexican weekend of the potential struggles Mercedes was likely to face at the Autodromo Hermanos Rodriguez.
"We've not had any particularly major dramas, it's just [about] trying to understand these tyres," he added.
"It was cool in the morning and then a bit warmer in FP2, and from the short run to the long run, it's just hard to pinpoint exactly how to get these tyres working. But that's the name of the game.
"I think we're not massively far off the Red Bulls, but the Ferraris, they just keep turning up their engine down the straights, the difference between us and them is massive down the straight line."
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