Red Bull’s Max Verstappen led Ferrari’s Charles Leclerc as Mercedes struggled in second practice at the Turkish Grand Prix.
Lewis Hamilton, who can clinch a record-equalling seventh title on Sunday, was fourth fastest, 0.85 seconds off the pace.
His team-mate Valtteri Bottas was third, 0.575secs behind Verstappen.
Mercedes were struggling for grip even more than everyone else on a slippery Istanbul Park track surface.
The circuit, which last hosted a grand prix in 2011, was resurfaced just two weeks ago, and bitumen leaking out of the track surface gave the circuit a sheen as cars ran on it on Friday.
This meant lap times were hugely slower than predicted – and even 13 seconds off those set in qualifying in 2011, since when Formula 1 cars have become several seconds a lap faster.
All the drivers were complaining of a lack of grip as a result, and there were a number of spins.
Despite Mercedes’ struggles in terms of headline lap times, there was strong evidence that they will remain the team to beat as they were comfortably quickest on the race-simulation runs late in the session.
“It was a bit of a disaster,” Hamilton said. “This is such a fantastic circuit and I don’t fully understand why they spend millions to redo a surface. I know it had been sitting around for along time, they probably could have cleaned it maybe, and now it’s worse than Portimao was (for the Portuguese Grand Prix last month) and the tyres aren’t working.