Title-chasing Hamilton eighth in FP1 in Austin
Lewis Hamilton did not show his pace in the first practice session at the United States Grand Prix, as Max Verstappen clocked the fastest time.
Hamilton will be sure to claim his third straight Formula One world title on Sunday unless Mercedes team-mate Valtteri Bottas wins the race.
Even a Bottas victory might not be enough to halt Hamilton, though, with any finish of eighth or higher enough to guarantee a sixth championship crown for the Briton.
If FP1 on Friday was anything to go by, though, it will be far from plain sailing for Hamilton, who struggled to find his best form on what he described on team radio as "the bumpiest track in the world".
After initially running on the development 2020 tyres, Hamilton switched to softs for his final laps.
But despite briefly moving into the top four, the two-time defending champion had a lap time deleted when he ran off the track, sending him back to 18th.
A late push saw Hamilton edge into the top ten, yet he was well over a second slower than leader Verstappen, who clocked a time of one minute and 34.057 seconds.
Meanwhile, Bottas was way down in 17th as Mercedes made a sluggish start to the week.
Verstappen, who was handed a grid penalty for failing to slow under a yellow flag in qualifying last week, losing pole position, had not one but two lap times deleted.
In total, nine drivers were penalised, with the track limit offences occurring at Turn 19.
Verstappen claimed to be "in [the] heads" of Hamilton and Sebastian Vettel on Thursday, and he led the Ferrari man in practice, with Red Bull team-mate Alex Albon completing the top three.