Lewis Hamilton was fastest in third practice for the US GP after the session was allowed to go ahead despite heavy rain lashing the Circuit of the Americas.
The conditions were so bad that spectators were not allowed through the gates for safety reasons. Yet even with the incessant rain that fell overnight and continued into Saturday morning, the FIA decided that cars were allowed to go out.
And, in front of empty grandstands, the cars went out - prompted by the belief that, should the conditions worsen for qualifying and force it to be cancelled, then the order will determine the grid for Sunday's race.
Speaking during Sky F1's P3 show, however, Ted Kravitz said FIA race director Charlie Whiting had indicated that, should conditions remain the same, then qualifying will start on schedule at 1pm local time (7pm BST).
Mercedes technical director Paddy Lowe said: "There is a very slim chance they will use P3 times as a grid if we can't get any sessions in before the race itself.
"So everybody was aware of that, which is why we saw everyone out there just trying to get a reasonable time on the board. So that put a little bit of tension into a session in a way you wouldn't normally have in the wet."
Sebastian Vettel was second fastest - although he and Ferrari team-mate Kimi Raikkonen are carrying 10-place engine penalties - ahead of Nico Hulkenberg, with Valtteri Bottas fourth from Carlos Sainz.
The top 10 was completed by Daniil Kvyat, Raikkonen, Daniel Ricciardo, Nico Rosberg and Felipe Massa.
Predictably there were plenty of spins, with aquaplaning a particular problem. Vettel spun three times on one lap alone as the rain intensified while Rosberg was lucky to escape damage worse than a broken front wing, caused when his Mercedes grazed the barriers.
He returned to the pits for repairs and stayed there - along with most of the rest of the field for the final 20 minutes or so.
Assuming the session does determine the starting grid, then Hamilton - the only driver to lap quicker than the two-minute mark - would start from pole, giving himself the best possible chance to claim his third title on Sunday.
There are conflicting forecasts for race day, with one suggesting showers during the morning - when a delayed qualifying session remains a possibility.
Practice Three times:
1. L Hamilton, Mercedes, 1:59.517
2. S Vettel, Ferrari, 2:00.380
3. N Hulkenberg, Force India, 2:00.496
4. V Bottas, Williams, 2:00.523
5. C Sainz, Toro Rosso, 2:00.687
6. D Kvyat, Red Bull, 2:00.694
7. K Raikkonen, Ferrari, 2:00.785
8. D Ricciardo, Red Bull, 2:01.008
9. N Rosberg, Mercedes, 2:01.474
10. F Massa, Williams, 2:02.199
11. S Perez, Force India, 2:02.660
12. R Grosjean, Lotus, 2:02.825
13. P Maldonado, Lotus, 2:02.825
14. F Alonso, McLaren, 2:03.375
15. M Ericsson, Sauber, 2:04.399
16. J Button, McLaren, 2:05.283
17. W Stevens, Manor, 2:05.378
18. A Rossi, Manor, 2:05.607
19. F Nasr, Sauber, 2:06.792
20. M Verstappen, Toro Rosso, 2:09.994