No running took place in the first 50 minutes of the session as heavy rain soaked the track, but as the rain eased more drivers took to the circuit in the final few minutes of the session.
A few hardy spectators had hung around at the track in the hope of seeing some running but they were not rewarded until Brendon Hartley took to the track in his Toro Rosso 47 minutes into the session, with more drivers soon following.
World champion-elect Hamilton emerged from his garage with just five minutes remaining and set a time 1.483 seconds quicker than Toro Rosso's Pierre Gasly in second place.
United States Grand Prix
Hamilton leads Mercedes one-two in wet US first practice
19/10/2018 AT 17:00

Lewis Hamilton of Great Britain and Mercedes GP prepares to drive in the garage during practice for the United States Formula One Grand Prix at Circuit of The Americas on October 19, 2018 in Austin, United States.

Image credit: Getty Images

The Frenchman ran on a fresh set of intermediates and reduced the deficit to Hamilton to just 1.012s at the end of the session.
Red Bull's Max Verstappen was third quickest ahead of Fernando Alonso, Nico Hulkenberg and Brendon Hartley. The Toro Rosso driver ran more laps than anyone else - 19 in total.
Hamilton's title-challenger Sebastian Vettel was only 10th quickest, nearly five seconds behind Hamilton.
Ahead of him were his Ferrari team-mate Kimi Raikkonen, Stoffel Vandoorne's McLaren and the Sauber of Marcus Ericsson in seventh.
Four drivers didn't venture out at all in second practice - Daniel Ricciardo, Romain Grosjean, Kevin Magnussen and Valtteri Bottas.
With more rain forecast for Saturday, teams preferred to save their wet and intermediate tyres for qualifying day.
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