Lewis Hamilton took top spot at the end of Friday practice at the United States Grand Prix, although the Mercedes' single-lap strength may not be all it seems.
Hamilton led Charles Leclerc and Max Verstappen on qualifying sim pace, but did so thanks to a helpful tow on his fastest lap.
Mercedes team-mate Valtteri Bottas was eight tenths of a second adrift and was bemused at the deficit to his team-mate.
Bottas must win to keep his faint championship hopes alive this weekend, but Hamilton will be crowned world champion for the sixth time if he finishes eighth or higher, regardless of what the Finn can do.
After an FP1 session that saw several drivers caught out by the bumps on the Circuit of the Americas, they played a role once again as Romain Grosjean ran wide at Turn 5 and lost his front wing in the barriers.
Sebastian Vettel also had a moment during his race simulations, but avoided serious damage other than scuffed tyres.