Lewis Hamilton set the pace at a rainswept Circuit of the Americas on Friday as Mercedes dominated first practice for a US Grand Prix that could crown him a five-times Formula One world champion.
The Briton needs to score eight points more than Ferrari rival and fellow-four times champion Sebastian Vettel on Sunday and a third successive Mercedes one-two finish would do just that.
Hamilton, who has won six of the last seven races and is chasing a fifth victory in a row, made an immediate statement of intent with a quickest lap of one minute 47.502, a hefty 1.304 quicker than team mate Valtteri Bottas.
Vettel was fifth on the timesheets with a 1:49.489, nearly two seconds off the pace, and behind the Red Bulls of Max Verstappen and Daniel Ricciardo.
Ferrari's Kimi Raikkonen was sixth fastest.
Hamilton won his third championship at the Texan track in 2015 and has been almost unbeatable in Austin, winning five of the six races there since Texas first appeared on the calendar in 2012.
With the rain coming down steadily overnight, but easing slightly before the day's action started, Friday's times were comparatively slow and Hamilton took his time before venturing out on track.
The session was briefly red flagged with 48 minutes remaining after Sauber's Charles Leclerc spun at turn eight and went off, scattering gravel across the track.
McLaren gave 18-year-old Briton Lando Norris, who will race for them next season, an outing in Stoffel Vandoorne's car and he was 12th fastest with double world champion team mate Fernando Alonso 11th.
Ferrari's Sebastian Vettel will have a three-place grid penalty at Sunday's US Grand Prix, dealing a blow to his hopes of preventing Lewis Hamilton winning a fifth Formula One world championship.
Race stewards decided on the drop after Vettel had failed to slow sufficiently while red warning flags were waved in Friday's wet practice.
Britain's Hamilton leads Vettel by 67 points with four races remaining and the Mercedes driver will take the title on Sunday if he scores eight points more than the German.