Lewis Hamilton set a searing pace as he dominated first practice at the United States Grand Prix.
The title leader’s Mercedes was 0.593 seconds quicker than rival Sebastian Vettel’s Ferrari, with Hamilton’s team-mate Valtteri Bottas third.
Hamilton will clinch his fourth title on Sunday if he wins the race with Vettel lower than sixth.
But he has labelled this idea as “silly”, saying he expects Ferrari will not have a fourth bad race in a row.
Vettel’s title hopes have been almost completely crushed by three consecutive terrible results in the races in Singapore, Malaysia and Japan, from two of which he retired.
Meanwhile, Hamilton has been in a rich vein of form that has seen him win four of the five races since Formula 1 returned from its summer break at the end of August.
Red Bull’s Max Verstappen ended the session fourth, on a day on which his team announced that he had extended his contract with the team until the end of 2020 in a deal that is believed to include a significant pay rise.
But Verstappen starts the weekend knowing he will drop down the grid as a result of Renault fitting an upgraded engine to his car.
Although it has not been officially confirmed, the Dutchman is to be given a new internal combustion engine which will mean a penalty for excessive engine usage.
The new engine is also being given to Renault driver Nico Hulkenberg, whose 20-place grid penalty was confirmed on Friday, and Toro Rosso debutant Brendon Hartley.
Their team-mates will not receive the upgrade for the rest of the season.
Hulkenberg ended the session 12th, two places behind new team-mate Carlos Sainz, who impressed on his first outing for his new team following his transfer from Toro Rosso.
The session started wet, with the drivers running on intermediate tyres for the first half-hour or so before gradually moving on to slick tyres.
McLaren’s Stoffel Vandoorne and Williams driver Felipe Massa were fifth and sixth after runs on the faster ultra-soft tyre while the four drivers ahead were on the super-soft.
Ferrari’s Kimi Raikkonen was seventh on the super-soft with the Force Indias of Esteban Ocon and Sergio Perez eighth and ninth.
Vandoorne’s team-mate Fernando Alonso, who was confirmed as staying at McLaren in 2018 on Thursday, was last having not set a time as a result of a hydraulic leak discovered after just three laps.
McLaren did get him out again before the end of the session but he managed only one lap before returning to the pits.