Lewis Hamilton beat Formula 1 world championship rival Sebastian Vettel to the fastest time in first practice for the United States Grand Prix amid mixed conditions at Austin.
The Mercedes driver clocked a 1m36.335s on the supersoft Pirelli compound tyres, 0.593 seconds clear of Ferrari's Vettel, with Valtteri Bottas half a tenth further back in third.
Early morning rain subsided before the start of the session, but the majority of the field headed out on the intermediate tyres for their installation laps.
Hamilton set the early pace on the green-walled rubber, with a 1m50.146s, but that was usurped by Max Verstappen when the Red Bull driver fitted a fresh set of the same rubber.
His teammate Daniel Ricciardo was caught out when he ran wide out of the final part of the high-speed esses and lost the car on the kerbs before catching it and continuing.
Felipe Massa then went quickest on the intermediates, but as conditions improved, Sebastian Vettel was the first to try dry tyres, running a set of supersofts to go quickest with a 1m45.960s.
After a lull in the running, Ricciardo broke the silence and posted a flurry of quick laps to break the 1m40-barrier with a 1m39.266s on the supersofts.
Verstappen demoted him briefly, before Hamilton sets his first time on dry weather tyres with a 1m36.935s to move top of the pile.
Hamilton improved again with a 1m36.335s to cement his place at the top of the timesheets with his time unchallenged for the remainder of the 90-minute session.
Verstappen, whose Red Bull team announced he would stay with the team until the end of 2020 on Friday morning, was fourth quickest, one second off the pace.
Stoffel Vandoorne, running an upgraded Honda power unit, was fifth quickest on the ultrasofts, but his McLaren teammate Fernando Alonso failed to set a timed lap and spent most of the session in the garage after the team discovered a hydraulic leak.
Felipe Massa was the leading Williams in sixth, with Raikkonen seventh and Force India's Esteban Ocon eighth.
Sergio Perez and Carlos Sainz, competing in his first session for Renault, rounded out the top 10.
Sainz was three quarters of a second clear of teammate Nico Hulkenberg, who will take grid penalties this weekend after Renault fitted an upgraded engine.
Brendon Hartley, who is set to start his debut grand prix from the back of the grid because of engine component changes, set the 14th fastest time, 2.932s off the pace.
The New Zealander was just under 1.2s quicker than Seal Gelael, who was running in the other Toro Rosso for this session in place of Daniil Kvyat.
Charles Leclerc replaced Pascal Wehrlein for FP1 at Sauber, clocking the 19th quickest time, just under fourth tenths adrift of teammate Marcus Ericsson.
|4||Max Verstappen||Red Bull||TAG||21||1'37.339||1.004||203.893|
|8||Esteban Ocon||Force India||Mercedes||25||1'37.808||1.473||202.915|
|9||Sergio Perez||Force India||Mercedes||20||1'37.861||1.526||202.806|
|10||Carlos Sainz Jr.||Renault||Renault||24||1'38.093||1.758||202.326|
|14||Brendon Hartley||Toro Rosso||Renault||28||1'39.267||2.932||199.933|
|16||Daniel Ricciardo||Red Bull||TAG||14||1'39.366||3.031||199.734|
|17||Sean Gelael||Toro Rosso||Renault||25||1'40.406||4.071||197.665|