Lewis Hamilton made the most of greasy track conditions to lead the opening Formula 1 practice session for the United States Grand Prix on Friday morning, outpacing championship rival Sebastian Vettel at the Circuit of The Americas.

Rain in the lead-up to the start of FP1 saw the majority of runners take to the track on intermediate tyres, with conditions gradually improving to allow drivers to venture out on slicks.

Vettel enjoyed a stint at the front before Red Bull drivers Max Verstappen and Daniel Ricciardo rose towards the top of the order, only for Hamilton to go faster than them all for Mercedes.

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A best time of 1:36.335 saw Hamilton finish half a second clear of Vettel, acting as a good early leg-up for the British racer on the weekend he could clinch a fourth world title.

Valtteri Bottas took third in the sister Mercedes, but was forced to pit with 15 minutes to go when an issue appeared on the rear of his car, causing his wing to wobble excessively at high speed.

Verstappen wound up fourth for Red Bull ahead of Williams' Felipe Massa, while Kimi Raikkonen wound up sixth-fastest for Ferrari ahead of McLaren's Stoffel Vandoorne.

The Force India duo of Esteban Ocon and Sergio Perez both breached the top 10, taking P8 and P9 respectively, while Carlos Sainz Jr. rounded out the top 10 on his first outing for Renault.

FP1 saw Brendon Hartley complete his first laps in an F1 car since 2012 ahead of his grand prix debut with Toro Rosso on Sunday, with the New Zealander finishing the session 14th-fastest.

Sean Gelael and Charles Leclerc also enjoyed run-outs as part of their development programmes with Toro Rosso and Sauber respectively, finishing 17th and 19th, while Fernando Alonso propped up the timesheets for McLaren after a hydraulic leak limited him to just four laps.