Championship leader Lewis Hamilton set the pace at a rain-lashed Austin after final practice for the United States Grand Prix went ahead as scheduled.
Bizarrely the session was played out in front of empty grandstands after fans were urged to stay away from the circuit on safety grounds with heavy rain continuing to batter the area.
But with the bad weather, which has plagued this week’s action, expected to continue throughout Saturday, qualifying could yet be cancelled. If such a scenario happened, the times recorded here might determine the grid for the race.
That would see Hamilton, who needs to outscore Sebastian Vettel and Nico Rosberg by nine and two points respectively to claim his third world championship, start from pole.
Hamilton’s best lap one minute 59.517 seconds was 0.863secs faster than Vettel, but the Ferrari driver will be hit with a 10-place grid penalty after changing his engine.
Rosberg, who damaged his front wing after losing control of his Mercedes through turn three, was only ninth, the best part of two seconds slower than his team-mate.
Nico Hulkenberg was third for Force India with the Williams of Valtteri Bottas in fourth. Carlos Sainz was next up in his Toro Rosso with Daniil Kvyat sixth in the standings.
Qualifying was still scheduled to take place at 1pm (7pm UK time). A decision as to whether it goes ahead will be made later on Saturday.
It had been anticipated that final practice would be scrapped after the circuit organisers urged fans to keep away, but, with no threat of lightning in the area, the session went ahead.
Rosberg was the first to fall foul of the conditions before Hamilton also went off the track at turn 17. Vettel lost control of his Ferrari on a number of occasions, and reported that the conditions were worsening as the session progressed.
Vettel’s team-mate Kimi Raikkonen finished in seventh with Daniel Ricciardo eighth, Rosberg in ninth and Felipe Massa rounding out the top 10.
The McLaren duo of Fernando Alonso and Jenson Button failed to capitalise on the inclement conditions as they placed only 14th and 16th respectively.